I bought a pack of rubbish bags at 7-11 yesterday. Didn't open it & had the receipt.
Went back to the same shop today, approached the staff at the entrance to show I came in with the item & asked if I could exchange for something else. She said yes.
Good, collected a few snacks and headed back to the cashier. Out of nowhere she says "cannot". Surprised I asked why and she replied "more than 1 day".
WTF. I bought a pack of plastic bags less than 24h ago, never opened the pack & cannot exchange ? I didn't even ask for a refund.
Then I insisted and told her that the other staff said this would be possible. The gates of hell then opened wide ensuing with swearing in Thai, angry faces and what not. Eventually she said "I give you money back". I said I can just get other items instead but she insisted I just get the money & leave the shop, as a punishment for my wrongdoings.
I left determined not to place a foot in that shop again.
Moral of the story:
1. A reminder that foreigners are welcome in Thailand only while they're walking ATMs. If you're actually asking for something back, well...good luck.
2. 7-11 has ridiculous unwritten (at least in English) policies. Caveat emptor.