This is probably the strangest or most random purchase story I have had so far. A couple of years ago, in a kid's activity center gift shop I found a couple of retired 8051 Technic Motorbike's for $45.99. I bought one and left one (was selling for about $120 at that time).
We were there again probably a year or so later, and they suddenly had 4 on the shelf. That time I bought 3, which all have sold in the $150-$160 range.
We returned again about 6 months ago and they had nothing.
I happened to be by there yesterday, so we popped in for a look, and they had FOUR of them on the shelf again! Picked up all 4 this time. It's a fairly rare set with very few for sale on Amazon/eBay, I have no idea where they keep finding these, guess I need to just ask how many more they have in the back. :-)