Older firmware psp advice
I've seen several people looking for PSP's with older firmware since they upgraded needlessly to 2.71.
While, besides doing a rather useless plug for my company, this is something that not many people know, or are comfortable taking advantage of, but it typically isn't any problema t all.
Go to a GameStop/EB Games, and if they are not busy (and you have the money to pick up the system in question if you find it), ask if they'll let you go through a couple of their systems for a downgradable firmware version. If they are pretty dead on customers at the moment, they probably won't mind helping you out, even if you let them know what is for.
Be sure to bring a list of what the serial numbers are for the base firmware of new psp's are htough, since you can't the systems for that.