I have a PSP that I bought but never used, and I thought I would. I have three games for it. Daxter, little big planet and clank. All od the games are mint and so is the device. How much would I sell it for? The standard price including the games or something different?

Which PSP is it? There's several different models. Did you get a memory card for it? If so and you're selling it with it, what size? What country are you in? Is the PSP imported? What about the games? Did you mod/hack the PSP?

You probably won't be able to sell something used for the same price you purchased it for, even if it is only slightly used. You would probably have to take at the very least a 10% hit.