I had a brief layover in the Frankfort airport a couple weeks ago - literally 1.5 hours. I bought a bottle of water at one of the shops and used my debit card. The shop employee spoke no English, showed me the total on the register, and gave me no receipt. I didn't think anything of it and used my card - perfectly normal transaction. Apparently, my debit card was overcharged about $69.
In trying to deal with the overcharge now that I'm back in the states, my credit union won't do anything about it because I don't have the receipt. Frankly, I NEVER get receipts if I don't have to, I often decline them when asked if I want one, and I certainly wasn't planning on keeping every receipt for every tiny purchase while I'm out, much less overseas.
So, I suppose keep this in mind when travelling - perhaps it's worthwhile to keep all receipts when travelling or just ONLY use credit cards that have a no-questions-asked policy regarding reimbursements.