:shock: do you eat em? are you careful with them out of the water? or maybe you need to learn to turn......
I think you probably are buying crap used boards. stay away from any used board whose glass has gone yellow(sun damage) or foam has gone brown(water seepage), has too many dings, has visible repairs (a good repair is nearly invisible), is missing most of its length, and is unusually heavy--meaning that the foam is waterlogged. all of these contribute to structural failure in the board.
I'd go invest in a good solid new board, of if you are hard on em, check out a tuff lite epoxy board by Surftech (
www.surftech.com) they are really poretty bombproof and come in various shapes and sizes.....