It's not very likely the panels were replaced for cosmetic purposes by a dealer. Most likely there was some wood rot issues that have either been repaired entirely or patched up to get by. It'd be hard to tell without being able to see inside the walls.
I have a Friend who has a late 80's or early 90's HiLo that he thought the lifting mechanism was broken. When I helped him remove the exterior aluminum to get to the mechanism, we saw that all the supporting 2x2's had dry rotted. There wasn't enough strength left in the wood to support the lift mechanism any more. He hasn't repaired it yet, it'll require a complete rebuild of the sides, still sitting under his shed.
Unless the price is so lucrative that you just can't pass it up or you don't mind taking the chance on internal wood rot, I'd pass on it until it can be unequivocally proved there isn't any hidden deterioration. Not sure how it could be proved without a tear down though.
'11 GMC Acadia SLT AWD
'11 GMC Sierra 1500 4x4 Extended Cab