If it were me, I would be pissed. You sound more 
forgiving than I. ^_^  As far as I've always been 
concerned, a deal is 100% closed as soon as a 
price has been agreed upon. Once a potential 
seller says something to the terms of: "Okay I'll 
sell it to you for $X" then that's the end of it. 
And *SHOULD* also be the end of any other 
dealings they have with anyone else regarding the 
cel in question.  Anything else is dishonest.

It would be different if the person was taking 
offers for a certain amount of time, but that 
doesn't sound like the case here. I hope you can 
either work it out with them, or find something 
else equally as nice for yourself. ^_^   I don't 
know how much you offered or for what cel it was, 
but if it were me, I would probably tell the 
seller off and keep my money. . . It would have 
to be a damn irreplacable wishlist cel for me to 
offer more after a move like that.

Many Sharp Smiles,
--Drac