The seller confirmed that the side art has yellowed. It's not horrible, but for what he's asking, I'd like to know I can clean it.
I guess it depends what caused the yellowing.
In my industry we call that "foxing".
It can be caused by a variety of things, ranging from oxidation to exposure to something.
If its exposure to something, like say cigarette smoke from being in a bar then you could probably clean it off as long as its not leached in and permanently stained.
If its oxidation from something like a surfer compound breaking down in the adhesive siding or ink, then its probably not reversible.
Sulfer in the chemical world is whats referred to as a sublime.
I.E. it can go from a solid state to a gas state without ever becoming a liquid.
It could be something like the adhesive used to adhere the side art contains sulfides and over time penetrated the side art staining it yellow. A sublime chemical will generally react faster with heat, so if that the case a hot climate might cause something like this to react faster.
You wont know for sure unless you got look at it.
I would say go look at it and find out.
Try cleaning or rubbing a small spot and see what happens.
Either way, looks like a good looking game to me.