Think about it.
You didnt mention if he was a business. He is probably not incorporated but could be classed as a sole proprietor; if so he is likely claiming his expenses as a tax deduction with his 1040 filing. Why wouldn't he want a bill of sale?
He is trying to maximize his tax write-offs and a Bill-of-sale with the sale amount you agreed upon reduces his tax write-off. He wants little income and much expense.
Lively, on track as usual. This is the only reasonable reason i could think of.
Do what you want with the bill of sale, but if it were me I would make sure everything was in order including the paper trail. Too much nonsense goes on these days and people will screw you for a nickle it seems.
Scorp