I had the experience of being told by someone not to shop in a store which I love and continued to patronize anyway. I later found out from a mutual friend, that the person who spoke to me had a bad experience because she tried to use an expired credit (over a year past the expiration date which was clearly printed on the credit slip) in the store, and the (new) owners explained they could not honor something that was issued by the former owners and had passed WAY beyond the expiration date. She became miffed, to say the least, and voiced her rather angry opinion of what they could do with the credit slip, and stomed out.
Personally, I feel a) it should be against the law to put an expiration date on a credit, since the money WAS paid and the services were not utilized and b) it is not good business to alienate a potential new customer for any reason. That being said, the expiration was printed in black and white in large letters, and the person should not have tried to pawn it off on the new owner, especially a year after it was not even valid.