Why does it have anything to do with "being weak"? The seller's

agent made a mistake and tried to make it right. Taking advantage of other's mistake has nothing to be proud of. (Like the other post, when the store gave extra clothes by mistake, it is an honest deed to return it back.)

This is different from if the seller, after a couple of weeks, realized that he could sell for more money and wanted to change the contract.

Of course, LZ can walk away from the deal if she likes.