Get to know potential subcontractors before accepting their bids, you might find that the combination of a low bid and a high maintenance subcontractor is not in your favor.

Make sure your subcontractor is properly insured-accidents happen and so do scams. If someone from one of your subcontractor's crews is hurt, who is responsible? If the subcontractor has proper worker's compensation coverage, the subcontractor's insurance is. If your subcontractor is without proper coverage, you may be sued.
If your subcontractor is not properly insured it suggests a couple of not-so-nice things about the operation. One is that they might not have the capital to pay for the insurance. An operation without much capital may be desperate for money. The other thing that it shows is an unwillingness to "play by the rules". Cutting corners as far as providing workman's compensation for employees might indicate that corner cutting is acceptable in other areas as well, like building your home.

Be involved in the project-if you are an owner/builder you need to be on the site and overseeing the subcontractors the same way that a general contractor would. You hire the subcontractors and they work for you. You have a right to act like the boss because you are. Find out what materials are being purchased. If you have questions about the pricing of materials go and check it out. If you are paying for four-dollar shingles, be sure that those shingles sell for four dollars. There are dishonest subcontractors and personable, likable people can be just as crooked as anybody else, or even more so.
Poke around all of the paper work and if you ever have any questions go should go immediately to the sub for answers. You should know everything about everything that is written on every piece of paper associated with your project. You should be especially diligent about everything written down with a dollar sign in front of it. An honest subcontractor will be able to give you straight answers without a lot of defensiveness. Consider defensiveness to be a bad sign.

Run a "tight ship"-the more organized you keep the operation, the less chance a dishonest subcontractor will have to rip you off. All paper work should be handled in a timely manner and all work orders and material orders should only be signed by you. Make sure that the work site stays clean and well organized. It is not uncommon that expensive tools "go missing" while several subs are working on one site. Avoid this problem by requiring that tools always be locked up when they are not in use.