 EXIF data from pictures
Just a little thought on eBay tracking your accounts. If you upload a photo to auctions, that photo contains a LOT more information than you think. It can contain the camera model, all photo settings, date taken, folder stored in, Camera Owner Name, uuid of the camera, and a lot of other information that could be ultimately used to identify you. I would not put it past eBay to read and store the EXIF data of all pictures uploaded to them and use it to sniff out duplicate accounts.
the good news is, this data can be manipulated or outright removed. I use GIMP as my photo editor (screw photoshop, this is open source and free) and when you do a save as for photos you've cropped, fixed, whatever, it has the option to keep or not keep the original EXIF data of the photo. I always strip mine, whether it be for eBay or not.
You find the GIMP here: GIMP - The GNU Image Manipulation Program | 
