Pick up bed dent a problem for a truck camper?

I wouldn't worry about that. So they tossed firewood or whatever in the bed, that's normal use of a truck. Like has been mentioned, it's just the sheet metal, it appears the crossmember is fine.
It's just a flesh wound. Heck wait till people start using those new aluminum Fords for anything but groceries!
If the truck is a dually, it'll carry that camper with no problems. And that's what it should be if carrying a camper is the main reason you're buying it!