1. Make sure that, no matter what, a professional gives you proof of his or her insurance.  Your property can be seriously damaged if someone who has no experience with power washing tries to do the job.

2. Whenever you can get references or testimonials from previous clients, it is a good thing. 

3.  Ask the contractor who will be power washing about any guarantees set in place.  They need to guarantee that their work will be good -- and it never hurts to see if you can get that in writing.  This should not be difficult, especially with a good company.  They should want you to be completely satisfied.

4. Research is always a good thing as well, so feel free to look into the methods that power washers frequently used.  Get up to date on some of the proper techniques, and ask any potential company which ones they use.  That way, you will know if your contractor knows what he or she is doing.

5. Also feel free to ask about how often a company works, whether full time or part time.  Full time companies may be more professional than others, and their contractors may have more experience.  A part time company may not have as many skills just yet.

6. Do not be taken in by clever marketing ploys, such as the so called hot water ploy.  Although this is used for commercial purposes, it is not needed for a residential structure.  In fact, it can do more harm than good by splintering the surface and making the wood "fur."

For example, hot water should never, ever be used on roofs made of shingles; doing so will make the shingles get soft and it runs the risk of washing many of the granules off of the shingles, leaving them unprotected.  Vinyl can be warped beneath an onslaught of hot water, which can be very detrimental.  In short, residential areas simply do not require hot water and a skilled washer is going to realize that and use a combination of cold water and high quality cleaning products.