You made a commitment so you honor it. Do you really want to blame this on religion?
The question is, is there a lav being violated here or not.
For the record I am expressly mochel and I do honor my commitments, both when buying and selling, as I understand it to be a implicit mechila when agreeing - the question is if everyone else does.
The fact that many people wish to back out of their commitment seems to indicate that they never agreed to such a scenario.
Since the kinyan did not yet take place, the buyer would have an issue of oonah unless there is mechila.