I think that it is sad we can't trust anyone any more. I think she was wrong in selling that before you were able to get back in a reasonable time as you had a deal!
I have heard stories about people making a deal to hold something on CL till they could get there and someone had called and offered them more money for it and they sold it to them. I think that is wrong too.
If I don't have cash at the moment I will offer them a check to hold till I get back with cash, they aren't out anything at all because they will get money if I come back or not and leaving a good check means I will be back with the cash and then I will trade the cash for the check back. Has worked well many times. Yes Cash is the best thing, but there are times I have stopped in at sales on the spur of the moment with no cash so if there is something I want I try and make a deal and then hope they stick with it. Sorry you missed out on your treasure.