Low ball these sellers. Find other contractors that are good with income/expense tracking and you should be able to get a good feel for what the "for sale" route is really worth. If they are bad witht the finances, they probably not only want to sell, but NEED to sell...badly.
Well it turns out that the seller & broker completely 'flaked' out on me and I have not heard from either in weeks. So I guess this deal is off. They were also pretty vague & evasive with providing real numbers or the process to get approved by Fedex as an ISP.