By the Copenhagen Theory of Ethics (https://blog.jaibot.com/the-copenhagen-interpretation-of-eth...), once you rent an apartment to someone for a particular price, you have a moral obligation to continue doing that forever.
Regardless, if you agree to rent $PROPERTY to $TENANT and I you want to sell me $PROPERTY, I don't see why I should be bound at all to any agreement with $TENANT outside of letting their current lease expire.
I don't buy that there is any moral obligation in the first place but to extend that to third parties seems a bit silly.