Be careful about who you choose to clean your concrete and other flatwork. ACME POWERWASH has over 12 years experience pressure washing in Arizona and we have seen plenty of damaged surfaces because homeowners and business owners chose to go with a cheap, disreputable "one-man band" company. Some of these "companies" use cheap or old equipment, cold water, and 0 degree tips which can carve out the "snail trails" you may have seen before on concrete surfaces.
A good pressure washing company should have clean, well maintained equipment, several years of experience, quality materials and chemicals, and carry all the appropriate insurance.
The pressure washing business is no different than any other industry, and the old adage applies: if it seems too good to be true, than it probably is. If a pressure washer is a lot cheaper than other bids you are receiving, they are probably cutting corners somewhere, and you could end up paying the price-even though you thought you were getting a deal.
Find more info at http://www.acmepowerwash.com.