HELP!!! Anyone bought a house from owner using lease to own?

Have a local property owner that does lease to own stuff. Make sure you cover missed/late payments. I spoke to one of the peolple that are now just renting from him. One of there payments was late thanks to the USPS trashing there payment and that voided there contract to purchase.....the owner of the property is a real *** clown.....but to be safe GET A LAWYER.....