Appearance Matters

The way a contractor presents his company says something about the attention to detail you can expect on the job. Don’t expect a suit and tie, but a contractor should have a neat and professional appearance. The contractor’s vehicle should display business signage and tools should be well maintained and tidy. The contractor should likewise have a business card and be willing to furnish proof of insurance, certifications, and references.
Related: All About General Contractors
Check Those References!

The best way to find a great contractor is to canvass family and friends for a recommendation. If that doesn't turn up a lead, request references from the contractor—and then actually check them! References should be previous customers who have had work done in the past year. When you call, check with these customers to make sure the work was completed on time, on budget, and using proper materials.
Contact Appropriate Agencies

Always check with the Better Business Bureau to see if any complaints have been filed against the contractor; you should check under the business name and under a personal name. If the contractor claims to be certified by a particular organization, check with that agency to confirm.
Related: Reading Between the Lines on Customer Review Sites
Get It in Writing

Insist upon a written contract. The contract should specify any costs for materials or subcontractors, and include a payment schedule. Avoid signing a contract that leaves open-ended amounts for products and materials—these are called “allowances" and can add thousands of dollars to the bill.
Document the Job

Check on the progress of your project frequently and keep a logbook or journal to document it. Supplement your notes with photos of the job at various stages. Protect yourself from scammers who substitute subpar materials by keeping track of the materials being used, and make sure that they are the same ones specified by the contract.
If It Sounds Too Good to Be True…

…it probably is. Be wary of low-ball offers and estimates that vary widely. Always get at least three estimates for a job, so you have a good idea of the “going rate." If a contractor offers a “one-time-only, special low price,” it is probably best to pass.
Related: Estimating Hints
Don’t Pay in Cash

Avoid contractors who work on a cash-only basis; they often are not paying taxes or may have something to hide. Pay by check, and pay no more than 20 percent of the total project cost as a down payment (some states limit the down payment to 10 percent). Never make the final payment until the job has been completed to your satisfaction.
For More...

For more home improvement tips, consider:
Don't Try This at Home: The 7 Most Dangerous DIYs
7 Ways to Skimp on a Kitchen Renovation
7 Ways to Skimp on a Bathroom Renovation
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