When I sold my round earlier this year, I drew up a contract which covered both sides. In it I stated the location of the work, how many customers there were and the turnover.
I added declarations that as a seller I relinquish the responsibility of said business to ..., and that the new owner assumed full responsibility ... etc. etc.
It may all sound boring, but both parties knew exactly where we stood, and were therefore protected from any later changes of thought that might create a misunderstanding on either side. I sold the work in 3 stages to the same guy using similar contracts. I was happy, and the buyer was happy as he knew exactly what he was buying, and that I would not try to regain the business by canvassing it back etc.
John