Be firm with people who are going to stuff you around, saying they'll take it, and then not putting down a deposit. If someone wants it, they need to back their talk with a CASH or a BANK TRANSFER, NON-REFUNDABLE, deposit.
It's not sold until money changes hands. Don't rely on verbal agreements. Write up a sales agreement that covers everything that might go wrong.
It doesn't need to be a 50 page agreement drawn up by a lawyer - just a simple handwritten agreement has authority in court, if major problems develop.
Ensure the description is accurate, that buyer has made himself/herself aware of all faults in the machine. Itemise the sale amount, the date, any terms such as deposit amount and when the balance is strictly due, specific sale conditions, if anything is included, or not included - and of course, both buyer and seller sign the document, and each gets a copy.
If you make the deposit non-refundable, you're covering yourself from losses of a sale to other potential buyers, who you missed out on, while the non-performing buyer was stuffing you around.
If a potential buyer makes an appointment to check it out, make yourself readily available - and don't put up with no-shows, and dreamers who want to talk about pricing without inspection.