Here are answers to some common concerns about home repair rip-offs.

What are some of the most common scams?

Roof and tree work scams are very common. In most cases, the consumer is overcharged, the work is unnecessary or work is done incompetently. It's not unusual for a firm to inflict damages surreptitiously that he can then offer to repair.

Another common scam has to do with left-over materials. For example, a man comes to your door offering you a great deal on resealing a driveway. He explains that he has material left over from another job nearby and doesn't want to haul the extra material away. You may think you're getting a great deal until you discover that your driveway resealing job was done with used motor oil!

Why doesn't the government at least shut down the firms that intentionally rip people off?

Generally speaking, this is something with which the government has had some success. Obviously, to be effective, the government needs to prove its case. That often depends on consumers fully reporting the situations they encounter. All too often, the consumer is too embarrassed to even report the incident. In other cases, the consumer may not even be aware that they were taken advantage of. Many scams are perpetuated by itinerant contractors that have no fixed place of business. These businesses keep moving all the time, frustrating the efforts of law-enforcement organizations.

What can customers do to protect themselves against con artists?

In order to stay ahead of the police, most scam artists cannot stay in any one place more than a few weeks. They don't have regular addresses and phone numbers. For most of them, that means they have to market themselves door-to-door. The good news is that, as a consumer, you can avoid the vast majority of these scams simply by refusing to hire firms that come knocking on your door.

Can customers ever trust workers who go door-to-door?

It is like playing with fire, and chances are that eventually you will get burned. These guys are professional actors who have become specialists at finding and pressing your trust buttons. In other words, they are experts at figuring out what makes you trust people. They then take that knowledge and put on a performance that matches your personal trust profile.

These guys are good. Their clothing, speech, manner-everything about them is designed to deceive you into trusting them. It's all an act, but a very good one. Taking chances based on your ability to see through the act of a professional actor is a very risky activity. Keep in mind that many of the firms augment their fake repair income with burglary. This means that while they are making fake repairs to your roof, they or their accomplices will also be looking for opportunities to grab cash, fine jewelry and other valuables.

Is checking with a neighbor a good way to determine whether a firm is reliable or not?

It's not a bad start, however, it won't really tell you very much. Even the most incompetent firms have happy customers. The real question isn't whether the firm has one happy customer, but whether the firm consistently pleases its customers. You are better off hiring the firms that please 95 to 99 percent of their customers. You can't determine that from one or two neighbors.

What's the easiest way to determine if a firm consistently pleases its customers?

You need to tap into an organization that tracks a firm's performance over time. Some clubs and civic associations poll their members and put together informal lists of recommended firms. This can be a great resource as long as the list is kept up to date and reflects current performance.

Contractor referral services do essentially the same thing in a more systematic way. It's much easier to check out a single contractor referral service and rely on it for referrals than it is to continually check out contractors and service firms on your own.

by David Hollies, reprinted courtesy of HomeAdvisor.com