Homebuyers are often in for a rude awakening when they receive their first property tax bill after they move in.

That's when they discover that the tax estimated at closing was just that: an estimate. More often than not, the estimate was not only off, it was way off -- by hundreds or perhaps even thousands of dollars.

Sometimes the bill is estimated by the real estate agent, who wants to show a low monthly payment so the place looks more affordable. Sometimes the agent simply goes off the seller's tax bill, not bothering to even hazard a guess of what the new tax bill will be when the house changes hands. Other times, the title company folks get it wrong. Even when they do their level best to get the number right, they are sometimes incorrect.

Whatever the case, the result is the same: The new owners are hit with higher house payments that they can't avoid. Unless they choose to sell and move on, they are stuck.

"Mistakes in property tax estimates can be much more than an inconvenience," says Mark Collins of Black Knight Financial Services. "In some cases, they can be devastating. Any unexpected and significant monetary obligation can create a substantial financial hardship."

Any number of things can drive up your property tax bill. The most likely event is a new and higher sales price, which means the value of the property has gone up. Another possibility: A pending assessment of property renovations or improvements is not yet reflected in the assessed value. Or an inaccurate or out-of-date tax record, overlooked until the property changed hands, may now be corrected.

The point here is this: Homebuyers shouldn't take anyone's word for it when it comes to their future property taxes. A little homework is in order.

Unfortunately, coming up with an accurate estimate can be difficult because there are so many variables to consider at the local, regional and state level, says Collins. There isn't any single solution that fits all states, since each state's tax rules -- and those of the jurisdictions within them -- present their own set of unique challenges.

The good news is that many jurisdictions offer free tax estimators on their websites. For example, Montgomery County, Maryland, has an estimator based on the address of the property and the tax account number for the most recent bill sent to the seller. Los Angeles County in California has an estimator for what you can expect to pay on your new house, but only for existing properties that are changing ownership, not for new construction.

There also are commercial sites that will do the same. Tax.Fizber.com, for example, is a free site that allows you to calculate the tariff for any property in any city nationwide.

If you are of a mind to do it yourself, your first step is to review the property record for your new house to determine whether the physical data accurately reflects the property in its current conditions. Is the correct number of bedrooms listed? Bathrooms?

Now determine if recent renovations or improvements are already included in the assessed value. If not, they will be in a future assessment. And if the work was done without the proper permits, it's highly likely that the current assessment in based on inaccurate information and that an increase is coming.

Next, according to New Jersey appraiser Michael Brady, determine if the assessment is disproportionately low (compared to like properties) by looking for the average ratio of assessed-to-true value for the taxing district. The ratio can be found in the Table of Equalized Valuations on the assessor's office website.

"Once you know the average ratio for your municipality, it's possible to evaluate the assessment to determine the likelihood of a future tax increase," says Brady.

The appraiser says this varies by state, and that not every state posts the equalized valuation table. But unless the jurisdiction updates assessments every year, there is likely an "equalization ratio" that is used to adjust assessments.

If the average ratio is near 100 percent, according to Brady, a purchase price significantly higher than the assessment is a strong indication that your taxes will be sharply higher. Ditto if the current assessment is significantly below market value, or what you paid for the place. So if the average ratio is, say, 75 percent, but the current assessment is 50 percent of value, a bigger tax bill is in order.

Sounds intimidating, for sure. But if you don't want to be hit by a major surprise, it may be worth a try. At the least, at closing, ask who estimated your tax bill and how they arrived at that number.

Erroneous tax bills can also trip up would-be buyers even before they close. The incorrect bill could be so high that buyers are turned down by lenders, because the tax puts them above the acceptable debt-to-income ratio.

Collins provides this example: A borrower who applies for a $500,000 loan is rejected because the DTI ratio is over the 44 percent his lender demands. But the ratio is high because the predicted tax bill is $6,250, as opposed to the actual bill of $5,000.

Had the bill been estimated correctly, the buyer would have been able to proceed. But the $1,250 difference kicks him over the ratio, and he loses the house he wanted to buy. Homework and preparedness can possibly help stave off this scenario.

What if they threw a housing recovery and nobody showed up?

That thesis is not exactly accurate: Millions of people will have purchased homes this year. Perhaps not at breakneck speed, but they are buying. According to the National Association of Realtors, existing home sales jumped 2.4 percent in October to a seasonally adjusted annual rate of 5.17 million.

Sales are now at their highest pace of 2014, but still remain 1.7 percent below the 5.26 million-unit level from September a year ago.

NAR maintains that the recovery won't reach its full potential until more builders get with the program. That's not to say builders aren't producing new houses; they are, but not at the number that's needed to satisfy latent demand.

According to the National Association of Home Builders, the nation's hammer-and-saw folks will erect some 990,000 new dwellings this year. That's up from 930,000 last year. But it's a far cry from the 1.4 million or more that are necessary to placate folks looking for a brand-new residence.

"In a normal year, there should be demand for 1.7 million units," Mark Zandi, chief economist at Moody's Analytics, said recently at NAHB's semi-annual construction forecast conference.

Of course, the economy isn't normal, at least not yet. So the "usual" number of enough people aren't visiting model homes and signing contracts. Particularly absent are the 3 to 4 million 18- to 34-year-olds who have yet to form their own households. They are either living with roommates, or in Mom and Dad's basement.

Zillow reports that 32 percent of all adults are now living with someone, up from just 25 percent as recently as 2000. Stagnant wages have been a major contributing factor in this. On average, Zillow found that doubled-up adults earn about 76 percent of the median income of people living on their own.

The percent share of first-time buyers continues to underperform historically. First-timers, according to NAR, have represented less than 30 percent of all buyers in 17 of the past 18 months. That's the lowest level in nearly three decades. Forty percent is the long-term average.

The share of entry-level buyers has been "well below normal" for the past seven years, according to NAR's chief economist, Lawrence Yun, who says builders need to raise their production by 500,000 units "just to open up" the inventory of homes for sale.

"One of the constraining factors is inventory," Yun explains. "First-time buyers tend to buy existing homes that owners vacate when they buy new homes. So builders need to build more so the natural chain reaction can begin. If we had more homes to sell, we'd make more sales."

But builders are an optimistic lot. Setting the 2000-2003 period as a benchmark for normal housing activity, when single-family production averaged 1.3 million units annually, NAHB economists expect single-family starts to rise steadily, from 48 percent of what is considered a typical market in the third quarter of 2014 to 90 percent of normal by the fourth quarter of 2016.

Put another way, the number of single-family houses built this year will hit 637,000 units, then increase 26 percent next year to 802,000 units, and reach 1.1 million houses in 2016.

That's still short of "normal" demand, but who's pushing it? Certainly not most builders, who were burned -- many into oblivion -- when the economy went south and they were stuck with too many unsold units.

"Single-family builders are feeling good," said NAHB Chief Economist David Crowe. "They are not overly confident, but confident enough to keep moving forward."

Realtors, on the other hand, aren't feeling so good. Even as the use of lockboxes hits a 12-month high, the confidence of NAR's members is at a 12-month low, Yun reported recently.

Yun said he can't decide what's more important: lockboxes or member sentiment. But in a few years, he added, the answer should be moot because a full recovery will have taken place and the housing market should once again be running on all cylinders.

For now, there are 2.3 million existing houses on the market, which is 6 percent more than a year ago, when 2.17 million units had "For Sale" signs in front of them. But it's not enough.

"The rise in doubled-up households is a troubling sign of the times and starkly illustrates one of the prime drivers behind weak sales," said Zillow Chief Economist Stan Humphries.

If there is a silver lining to all this, it's that all of those roommate households "represent tremendous energy for the market," said Humphries, who figures a half-million buyers are waiting in the wings to step into the market as the economy trudges forward.

Credit unions reached a pair of milestones recently, and that's good news for homebuyers.

The nation's 6,557 credit unions passed the 100 million-member mark in June, according to the Credit Union National Association. But more importantly, at least to the housing market, CUs have posted a 10 percent year-over-year increase in mortgage originations as of the first half of 2014.

That means these service-oriented, member-owned cooperatives now have more than an 8 percent share of the home loan market. That's three times what it was prior to the recession.

Granted, purchase-money lending by other institutions is way down, which automatically gives credit unions a larger share. But there's no doubt that while other lenders are losing business, CUs are boosting theirs.

Nearly two-thirds of all credit unions offer mortgages, and those that don't offer them tend to be very small. So some 98 percent of the vast credit union membership is affiliated with institutions in the mortgage business.

Mike Schenk, vice president of economics and research at CUNA, says his members have posted huge membership gains, in part, because they offer financing for new and existing houses.

"Definitely mortgages have played a significant role," Schenk says. "We've seen a very strong increase in originations over the course of the last several years."

Indeed, mortgages currently account for 41 percent of all credit union loans, as opposed to just 25 percent in 2000.

Credit unions are not-for-profit institutions that are controlled by their members. They were first introduced in 1909 to combat the loan sharking and high interest rates that were common at the time among financial institutions serving the working class.

These days, you still have to be a member to borrow money, whether for a house, car or boat. But if you don't have a credit union at work, there's probably one in your local community. Many are either tied to a church or are trade-related -- that is, oriented to an association, organization or union. And most are hardly what you'd call exclusive, meaning that practically anyone can join.

There are several reasons why CUs have gained ground in the mortgage space, not the least of which is that they answer to their members, not a group of outside stockholders demanding a high return on their investments.

"As members, you are the primary focus," says Schenk. "If you have an account, you are an owner and you have a voice in running that institution."

During the financial meltdown, moreover, credit unions refrained from making the toxic, consumer-unfriendly loans that took some lenders to the brink of failure and pushed others over the edge. That's why charge-offs at CUs were only a fourth of what they were for other lenders.

Furthermore, when other lenders hunkered down to weather the recession, credit unions tended to remain fully engaged. And as a result, according to research, consumers trust CUs more than other banking institutions. "People really do realize CUs are acting in their best interest," says the CUNA economist.

Many also realize they can save a bunch of money at their credit union. They usually aren't any cheaper when it comes to interest rates, but CUs tend not to tack on a bunch of superfluous fees that other lenders seem to love.

And because they are local and member-controlled, they are more likely to consider applicants with a story to tell than some underwriter five states over who is forced not to deviate from standard guidelines.

The typical loan amount at credit unions is $130,000, and 70 percent of their loans are the garden variety, plain vanilla, 30-year fixed-rate mortgage. But that doesn't mean they can't be innovative. Several are.

This spring, for example, Mountain American Credit Union, the second-largest in Utah with 488,000 members, was the first mortgage lender in the country to actually close on an electronically signed FHA loan. And earlier this fall, the pioneering CU closed on the first e-signed VA mortgage.

A few more examples:

-- Pentagon Federal, with 1.3 million members nationwide, pioneered a 5/5 adjustable mortgage in which the rate resets every five years to the market rate at that time. Then the Alexandria, Virginia-based institution gave us the 15/15 ARM, which adjusts only once, at the midterm mark.

-- Then there was the five-year fixed-rate mortgage from the 41,000-member National Institutes of Health Federal CU. Dubbed the "see ya" loan, it was basically a refinance product so owners could time a special event -- retirement, for example, or when the kids start college -- to the end of their mortgage payments.

Bottom line: If you've overlooked credit unions as a source of financing, look around. Join one and see what it has to offer.