Unlike the front side of the rim, especially on a front wheel drive car, which is heavily supported by the mounting disk of rim, the back side of the rim can deform under severe impact.
I bought a set of used TL rims a couple of years ago, one rim had a very slight deformation on the inside edge, which is inperceptable without measuring on the Hunter machine, I took it to a wheel refinishing shop and watch the fellow put it on a turntable, clamp it down, and gentlely heated up the area around the deformation, then used a hydralic press to straighten out the deformation. Cost me about $60 IIRC.