No shop can afford to perform any work on your equipment without charging something for their effort. Of course, most shops will reduce the cost of any repairs performed by the amount of the prepaid estimate. Don't look for the cheapest shop . You can expect to pay about the same hourly labor rate for computer repairs as you do for repairs to your automobile. Don't pick a repair shop from the phone book.
Good shops advertise in the yellow pages, but so do the bad ones.
In the absence of local references or major chains, check with the Better Business Bureau, the Chamber of Commerce, the Department of Consumer Affairs or equivalent, and the State Attorney General. A minor computer repair can become a major ripoff if you don't choose your shop wisely. Don't sign anything you haven't read and understood yourself. Unscrupulous repair dealers prepare unscrupulous contracts. Read the fine print and get a copy of the contract.