For my part, a guy from United Kingdom bids and wins a lot of 4 ancient Roman coins, with very sharp and detailed pictures of both sides of the coins, and I always write "These are the coins you will receive".
The guy has 8 or 9 feedbacks, one negative from another ancient coins seller saying "Buyer thinks coin is a fake, left negative, then decide he likes the coin", or something.
Not a good start. I ship anyway, my coins are authentic and I ship within 24h, it should be fine. Four days after I shipped, he send email : "You sent different coins than pictured. Why?"
Seriously, I am almost paranoid about making a mistake, my system is perfect, I never mixed orders, I double check, triple check orders before to ship!
Also, four days to UK ? That is fast delivery, for $1.92 Canada Post Light Packet! Hard to believe...
I emailed the guy, asking him to scan the coins and email me the file, to compare with order, and try to find out who's the other buyer about to receive wrong coins too! Of course, I knew it was impossible, I just wanted him to go further in his lie, to see if he was smart, some kind of scam artist...
He left positive feedback a few hours later, a very nice comment about the service.
What do you know...