The best way is to work the round together and do the deal after its all worked.
Its the safest for both parties.
But saying that we've purchased work and not done this, handed over the cash and worked it with no problems, we've also handed over 50% worked it and then paid the remaining a month later, and we have worked with the seller.
I bet we have done this at least 20 times and all has been good, we have been burnt once though, completely our fault but we we're just buying stuff quick and took our foot off after having so many hassle free round purchases.
I think after an initial conversation with a buyer you can tell if they are legit anyway
Also depends how much youre talking about ££££.
Remember you still have all the customer names and numbers so if it goes sour you can call each customer and explain hes not taking over now and you are the cleaner still, messy but an option if it went this way.
If youre working it with him just take payment when all the jobs are completed.