Autocheck and CarFax and the like are by no means perfect. As you are finding out, they can be a rather large liability to the seller. AFTER the fact.
My last car had a “clean” CarFax and I have since found the right rear fender has been repainted and the rear bumper cover as well.
I’d suggest arguing with the dealer that even with an accident or 2, the truck is in good shape and/or repaired well. Good repair work, to me is more important than the accident itself.
It might be worth talking to a lawyer.