If you are going to eBay the games, you will be better off selling them individually. These will all work on other models besides the A500 too.
If you are going to auction them, don't start the price too high - it'll scare bidders off - If you use BIN, go for what you think it will bring.
Try to hit it when posting is free - it can make a real difference in overall cost to you.
Good luck