Corporations can include whatever paperwork that they like,but the fact of the matter is that it is not legally binding. Once you have bought the product you have the right to resell it at a later date. Duplicating and P2P sharing are obviously illegal. The resale of the original product is not. I do not blame ebay for cooperating with companies who complain about their products being resold,they probably do not need the hassle.
But what next book and music publishers going around charity shops insisting second hand goods being removed from sale!
Incidentally I have had great results from Centerpointe over five years. But I agree that they are way overpriced.