I buy and sell collectible cards (very small playingcard-sized items that fit in a regular envelope). Some sellers from the US charge 75c to ship within the US, and $4 anywhere else (including Canada), even though it costs them a 47c stamp to mail within the US and a 60c stamp to mail to Canada. Gross.
I've had "buyers" email me with stuff like:
"Hi. I don't want to buy your stupid cards, but I will, if you promise to leave positive feedback, and have it in my hands within 3 days. If not, I'll report you to eBay, and give negative feedback. I don't trust people on eBay, I've been burned before by jerks like you, etc. That's why I'm so cautious. Reply asap or else. Thanks!"
This comes after ZERO previous contact with the person. Just right out of the blue. Makes you feel kind of vulnerable, when everything you sell is BIN and these people can buy stuff and have you at their mercy, on a whim.