How does the seam look and feel absent that window light? It's not a fair angle to subject a carpet seam to. It's not always possible or reasonable to avoid seams that are in awkward lighting angles. Neither can every seam be completely invisible at any angle under any lighting conditions.
But you know all that. Just sharing my thoughts and trying to help you structure your argument to the store, client, inspector, insurance agent, lawyers and judge should it go that far.
I got sent to repair a few seams in the Occidental Petroleum corporate headquarters on Wilshire Blvd. in Los Angeles. It was a theater setting and the complaints were about the seams in a corridor leading to the theater where I think they did corporate trainings and such. Anyways there was no overhead lighting down the halls only lights setting about a foot off the ground on the walls of the corridor every 10' or so. The low angle lighting highlighted the seams........your situation exactly.
I knew the guy who did the install-----best carpet layer I ever met. Still, I ran my all down the seams to see if there was any gaps, trapped yards or whatever. There wasn't a damn thing wrong with the seams. Nor was there a damn thing I could do to improve them. You can't close the lights in a room and shine a light angled low onto a seam. Many, if not most seams WILL show under that light. It's the nature of the beast.
I respectfully refused to open up the seams and re-burn them. If my buddy Jack couldn't make them happy sure as hell I couldn't. They understood and the case was closed.
Some people can be convinced of what we here would all understand if the argument is presented convincingly with the proper attitude. The idea that they "threw you under the bus" indicates to me the person handling the customer might not be the right man for that role. And that sucks for you.
