Quoted from tpellowe:Go with the Bill of Sale -As Is - No Warranty stated nor implied. Game name, year, serial number, make, sign, date. Done. I have never done this however not bad practice.
I've had a few people who requested a bill of sale but more importantly I had to produce a few when buying my house because they couldn't "source" some of the money (a bunch of b.s. hoops we all have to jump through after the housing collapse e.t.c.)