I don't even bother with "leasing" per se. In my opinion the best option is to give them the option to finance it. I use Epik and have absolutely 0 complaints.
So if I was in your situation for example, I would sell it to them for $5,000 with these terms:
$500 initial payment via paypal to being the agreement. Then once payment is received, set up the lease in Epik. You can choose between 1 month and 5 years, which is up to you to decide with the buyer beforehand.
Say you decided on 1 year, you would set the monthly payments to $375 with the option to buy out at $4,500. Then for additional terms, "The cumulative lease payments will be applied to principal at the time of the purchase."
So now you don't have to worry about a potential buyer coming along while the domain is being leased. And if for some reason the buyer backs out or doesn't make payments, you still have the domain + $500 + any payments that have already been made.