I like the reverse. Like when someone decides a cheaper price of a figure FOR you even though you are selling it at actual retail price. Those annoy me. I once picked up a figure for someone on another board, someone that I had dealt with in the past without issue. He knew the price since I told him before I picked it up and when I got it he said he didn't want it anymore. No biggy, I can sell it. So next moth I list it on a site and he asks for it at a cheaper price and I haven't spoken to this person since.
Love those kinds of people. (sarcasm overload) Do them a favour and they pull shit like this. Mind you this was years ago but I find it just as annoying as people who scalp.
Edit: Curious as to how much MP TRU Grimmy is selling for on ebay, stumbled upon this
http://www.ebay.ca/itm/TRANSFORMERS-TRU-Toys-R-Us-EXCLUSIVE-MASTERPIECE-GRIMLOCK-Sold-/321076360912?pt=US_Action_Figures&hash=item4ac1a47 6d0
Used AND broken.