This is part 4 of the series. Thank you to National Association or Realtor for this article.

Protect yourself against contractor scams that threaten to stick you with shoddy workmanship or take your money and run.

The vast majority of contractors are honest, hardworking professionals. Protecting yourself against the few bad apples requires checking references, having a solid contract, and being alert to the warning signs of these top five contractor scams.

Scam 1: I’ll need the money up front

This is the most common ruse reported to the Better Business Bureau. Your contractor explains that because he has to order materials and rent earthmoving equipment to get the job started, he needs, say, 30% to 50% of the project price up front. Once you’ve forked over the dough, one of two things happens: He disappears on you, or he starts doing slapdash work knowing that you can’t really fire him because he’s sitting on thousands of your dollars.

How to protect yourself: Never prepay more than $1,000 or 10% of the job total, whichever is less. That’s the legal maximum in some states, and enough to establish that you’re a serious customer so the contractor can work you into his schedule—the only valid purpose of an advance payment. As to the materials and backhoe rentals, if he’s a professional in good standing, his suppliers will provide them on credit.

Scam 2: Take my word for it

When you first meet with the contractor, he’s very agreeable about doing everything exactly to your specifications and even suggests his own extra touches and upgrades. Some of the details don’t make it into the contract, but you figure it doesn’t matter because you had such a clear verbal understanding.

Pretty soon, you notice that the extras you’d discussed aren’t being built. When you confront the contractor, he tells you that he didn’t include those features in his price, so you’ll have to live without them or pony up additional money to redo the work.

How to protect yourself: Unfortunately, you have no legal recourse because you signed a contract that didn’t include all the details. Next time, make sure everything you’ve agreed on is written into the project description. Add any items that are missing, put your initials next to each addition, and have the contractor initial it, too—all before you sign.

Scam 3: I don’t need to pull a permit

You’re legally required to get a building permit for any significant construction project. That allows building officials to visit the site periodically to confirm that the work meets safety codes.

On small interior jobs, an unlicensed contractor may try to skirt the rule by telling you that authorities won’t notice. On large jobs that can’t be hidden, the contractor may try another strategy and ask you to apply for a homeowner’s permit, an option available to do-it-yourselfers.

But taking out your own permit for a contractor job means lying to authorities about who’s doing the work. And it makes you responsible for monitoring all the inspections—since the contractor doesn’t answer to the inspector, you do.

How to protect yourself: Always demand that the contractor get a building permit. Yes, it informs the local tax assessor about your upgrade, but it weeds out unlicensed contractors and gives you the added protection of an independent assessment of the work.

Scam 4: We ran into unforeseen problems

The job is already under way, perhaps even complete, when this one hits. Suddenly your contractor informs you that the agreed-upon price has skyrocketed. He blames the discovery of structural problems, like a missing beam or termite damage, or design changes that you made after the job began.

The additional fees might very well be legit, but some unscrupulous contractors bid jobs low to get the work and then find excuses to jack up the price later. If you’re unsure whether your contractor is telling the truth about structural problems, you can get an impartial opinion from a home inspector, the local branch of the National Association of Home Builders, or even your local building department.

How to protect yourself: Before signing the contract, make sure it includes a procedure for change orders–mini-contracts containing a work description and a fixed price–for anything that gets added to the job in progress. The extra work, whether it’s related to unforeseen building issues or homeowner whims, can proceed only after the change order is signed by both homeowner and contractor.

Scam 5: I’ve got extra materials I can sell you cheap

This hoax is usually run by driveway paving companies, whose materials—hot-top asphalt and concrete—can’t be returned to the supplier. So the crew pulls up to your house with a load of leftover product and quotes a great price to resurface your driveway on the spot.

Even if it’s really a bargain (by no means a sure thing), taking them up on the offer is risky if you have no idea who they are and haven’t checked references. And if the driveway starts cracking next year, you can bet you won’t find this bunch again.

How to protect yourself: Never hire a contractor on the spot, whether it’s a driveway paver, an emergency repairman who shows up after a major storm, or a landscaper with surplus plantings. Take your time to check contractors out to make sure they have a good reputation and do quality work.