Deposits on parts

If they need you to hold it, then I would take 20% down on 500 dollar items or more and hold for 2 weeks. If full payment isn't received within the 2 weeks, item goes back up for sale and you keep the 20%. Should they get the rest of the money before you sale it again, then they pay the 80% and deal done. Personally, I wouldn't take "hold money" on less than 500. Under 500 pay in full.