not legla advice, but what about a rent contract with really strict terms in addition to the big deposit. something like, “in the event the sale of the house fails to occur, and the buy is still in the property living under the terms of this Lease, and it becomes necessary for the Seller to evict the buyer because the Buyer refuses to vacate, then the Buyer agrees that the Seller shall be entitled to liquidated damage sin the amount of $50,000.00. Witha big deposit and a big judgment hanging over their heads, they’d probably leave. maybe. unless they were real deadbeats. but if they were just looking for a free rental, they wouldnt agree to termsliek that. maybe. get your own legal advice.