Lots of good advice given, like selling in a safe place (i.e., the police station or some other public and well-lit location). I would add:
- Take someone with you
- have the buyer sign a pre-written receipt that you can bring with you, which includes the price, a picture of the amp, the amp’s serial number, and a statement that the amp appeared undamaged and that they paid you in cash
- photograph the amp and box while you are at the transaction
- have your friend discretely record the buyer’s license plate number
- Have the bank check the bills if you want - although I probably wouldn’t go that far unless something felt totally off (can you purchase one of those markers that detect counterfeit bills? - all the party stores have them)
- remember you can walk away with the amp if something freaks you out
- if you are paid in all $1s then @bkeske was right…stripper, if you get paid in some $1s but mostly $5s and $10s then…a more successful stripper…maybe bring a chair and give yourself some extra time 😎