The fact that the safety features like the seatbelts and the head rests don't work properly is concerning. That after the accident/s it was in, these were not repaired or replaced properly. I would get an estimate of the repair costs from the collision repair specialist and mention that to the dealer, to possibly get the price down. You want those working correctly in a rear end accident.

If the body damage is only on the bumpers, it's probably fine rust wise, just cosmetic damage, since bumpers are made of plastic. The damage near the wheel though, someone ran into that area on my car, and it damaged some parts of the wheel that would have caused problems down the road. The person who ran into me only wanted to pay for the scratched paint, my insurance jumped in and advocated to get the wheel repaired also. My understanding is it was out of alignment plus some other damage, and would have caused uneven tire wear, or worse, could have caused an eventual blow out. So it was a safety issue to not repair it.

So Toyotas are reliable, and they tend to not rust. The interior looks really clean. I prefer cloth interior over leather. It looks like it wasn't being used to haul a bunch of kids around. For safety reasons, I would definitely heed the recommendation on the Carfax and get it checked out by a collision specialist.