They seem to do that a lot. I made an offer on one just Friday that was on
DVC Shop listed as "new" and the lady responded the next day that she had just finalized a sale on it (the agreement anyway, it hasn't been to ROFR but at that point in my mind it should be considered unavailable as either the buyer or DVC will be taking it).
It's making shopping tough because I hate to make more than one offer at a time. I sure don't want to end up getting two offers accepted because I just can't buy that many points at once, and I wouldn't feel right about bailing on an offer I make. I'm sure the sellers wouldn't appreciate that either.
The time between making an offer and finding out it is already taken puts me at a disadvantage on other contracts that I am holding off on making an offer on. I'm on my third offer in 2 days and the ones I like seem to go pretty fast.