KPMG would be expensive, maybe you could get a local firm to do the same work, its fairly routine stuff.
You should look at the industry and make sure its growing just as the seller is claiming, check out the competitors and see if they are making money and how good an operation do they run.
Make sure there are no skeletons lurking in the business, e.g. has a key member of staff left recently? are all taxes and returns upto date, have rates been paid (often one of the last bills to get attention) are there any insurance or legal claims pending, these can often be hidden from the sale.
Bear in mind if you buy the company, then you are assuming all responsibilities for the last seven years. Think about that one, maybe you'll want guarantees from the sellers for a few years to allow any nasties to come out.
Finally, appoint experts to get the routine analysis done and you should research the big picture, e.g do you like the business, hours of work, is there growth, is there profit?
hope this helps