Another random anecdote.

We ordered a custom glass shower door from Lowes because we were remodeling.

During the process, we found we were happy with a curtain (which we did not have before, we were replacing an existing door).

So, we asked Lowes if they would take it back, and they did.

A custom sized, $1500 door -- and they took it back. We were really surprised and grateful for it, to be sure. No idea what the aftermarket is for random sized shower doors.