The seller has your thank you assuming it was not a short sale....they have your money, and hopefully at closing there were the traditional "congratulations". There may be issues with the house yet, and if you send a thank you, that could be deemed to undercut any future claim you may have. If you want to do something, drop off a box of donuts to their new place, but don't put anything in writing quite yet..... You can always do so in a year saying something like, you know we haven't forgotten you, etc. Point: I bought a house, had a full inspection.... the sellers left all sorts of things we thought were nice, and a month later it flooded...and they should have known - FRAUD!!!!!!! I later sold the house and thought I had left it in much better shape, and even brought over some donuts myself to the buyers. A few months later the buyers were threatening a lawsuit claiming I failed to disclose something that was OBVIOUS, and they also had an inspection!!!!