When I was about 12 (I'm 19 now) I had a real thing for bubblegum. One day, in my lunchbreak, I went to the shops nearby to stock up. I was buying about fifteen packs of bubblegum.
Because the shop was so close to the school, a lot of my classmates were around. One of them (who I only vaguely knew by sight) reached over me, grabbed one of my packets of bubblegum and then ran out of the shop. Rather than chase her, I just picked up another packet and added it to the pile. The shop assistant then added another packet of bubblegum to my total. When I asked why I was being charged for someone else's shoplifting, she said "you'll have to take that up with her".
I did buy the bubblegum in the end (I was a shy and retiring little pre-teen), and someone eventually forced the girl to give the packet back. Nowadays, I'd refuse to buy anything; someone else steals something, she sees who it was, and then charges another customer for it? o_O
I also figured out later that she'd charged me too much for each packet of bubblegum - 17p rather than 15p. Fortunately, she couldn't count, so she'd charged me for less packets than I had anyway; worked out about even.