that's assuming there is frame damage. A minor fender bender is unlikely to have frame damage.
Correct, most vehicles that have frame damage you can tell, it's almost impossible to put back a vehicle frame like it was before any damage.
if there is frame damage in the front of the vehicle just by opening the hood or measuring the gaps from the hood to the panel's you could see if it's off.
and the same with the trunk if it's a car remove the spare tire and look inside if you see any welding or misaligned panels.
Hard to hide.