Make sure there is a genuine good reason for why he` selling,i don`t know any WC that would sell work if it was cream.99% of work for sale is average at best from what i`ve seen in the past,like i say check out reason for selling and try and get him to back it up,also look through the list of work and pick a couple out at random,call on those houses and see if there willing to let you continue this will give you a better feeling as to what your buying.