Most of us couldn’t afford to buy a house without a mortgage. But having a mortgage makes you vulnerable to a growing list of loan-related scams. 

These can be complex, and the people who commit them aren’t always easy to spot. They may even appear to be upstanding members of your community. According to the FBI, “a high percentage of mortgage fraud involves collusion by industry insiders, such as bank officers, appraisers, mortgage brokers, attorneys, loan originators and other professionals engaged in the industry.”

Here are four of today’s mortgage frauds and some warning signs to watch for.

Related: Safest and Riskiest Mortgages

Mortgage relief scams

If you’ve never had trouble paying your mortgage and you never expect to, you can probably skip this one. But if you’re living from paycheck to paycheck, have little money in reserve or your job is in jeopardy, read on.

Since the housing crisis began in 2007, con artists have developed numerous ploys to separate people who can’t keep up with their mortgage payments from whatever cash they have left. They promise to help you reduce your debt and keep your home — in return, of course, for a substantial fee. The crooks may contact you by letter, or you may see advertisements or fliers promoting their phony services.

For example, the Federal Trade Commission (FTC) says, someone may offer to negotiate with your lender on your behalf, once you’ve paid an upfront fee. Or you may be asked to send your mortgage payments to the fraudster instead of the bank while the matter is supposedly being negotiated. Either way, of course, you won’t get any real help (and you’ll never see your money again).

In another variation, the FBI says, a scam artist will pretend there’s a class action lawsuit in the works against your lender to get borrowers’ payments reduced. You can join the fake suit by — you guessed it — paying a fee.

Warning sign: The FTC points out that under the Mortgage Assistance Relief Services (MARS) rule, it’s illegal for companies to collect fees from you until your lender agrees to a change of terms and you’ve accepted it. So consider any request for money in advance a warning.

Fake servicer scams

The company that collects your mortgage payments, your mortgage servicer, may be different from the bank that issued your mortgage in the first place. Over the years you have a mortgage, you may find yourself dealing with a succession of servicing companies.

That has created an opportunity for criminals, who send out official-looking documents telling homeowners that their account has been transferred and they should now send their mortgage payments to a different address. Of course, any money you send them will just go into their pockets, and you may also find yourself delinquent in paying the real servicer.

Warning sign: A letter claiming that your account has moved isn’t necessarily a red flag because that can also happen for legitimate reasons. But to avoid being cheated, the FTC suggests calling your old servicer and asking whether the switch is on the level.

Related: 5 Smart Ways to Protect Your Credit Score

Mortgage identity theft

If they have enough of your personal info, thieves may be able to use your identity to get a loan to buy a home. That can leave you on the hook for debts you knew nothing about and inflict serious damage on your credit report.

Or, they may be able to take out a home-equity loan or reverse mortgage on your home and pocket the proceeds. You’ll be responsible for the fraudulent debt, at least until you can get the situation resolved, and might even face foreclosure. The reverse mortgage version of this scam typically preys on elderly homeowners.

Warning sign: If you receive a payment booklet or other material in the mail from a new mortgage company, follow up with that lender, the FBI says. If you suspect you’ve been the victim of mortgage identity theft, or any other kind, the FTC has some step-by-step guides for what to do next.

House stealing

That’s the FBI’s term for what it once called “the latest scam on the block.” The person either cons you into signing over the deed to your house or impersonates you and signs your deed over to someone else. The “someone else” could be a buddy of the scam artist or another innocent victim, who thinks he’s buying a house from the actual owner. Not knowing that any of this has happened, you may continue to make your mortgage payments, unaware that you’re paying for what is now someone else’s property.

House-stealing scams often victimize older people. The perpetrator may even be a relative or friend of the victim.

Warning sign: Watch your mail for any communications from mortgage companies, regardless of the name they’re addressed to. The FBI also suggests periodically checking with the local government office where deeds are kept on file to make sure nothing suspicious has happened to yours. 

Related: How to Avoid a Reverse-Mortgage Scam

Greg Daugherty is a longtime personal-finance writer and a former senior editor of Money magazine.