Seller-financing to a foreign-national

Hey all, I received an offer on a house I built with a construction loan through seller-financing. The reason for this is the buyer is a foreign national and can’t purchase property in my region until they get permanent residency. So the buyers offer that they will pay a 20% non-refundable deposit and interest only on the the remaining 80% and if they get their Permanent residency within 2 years they will pay the full 80% in cash. If not, they forfeit their deposit and I can put thr house back on the market. What do you guys think about this offer, it seems fair to me but I’m a bit wary.