Steve I have a platinum GBA SP - the screen is in good condition but you can definitely tell the system has seen some play. Some scratches on the top of the unit, and on the playing area. Some small spots where it looks like the paint is rubbing off? It doesn't look bad honestly, but it definitely doesn't look mint.
I played this sucker a lot before I upgraded to the DS. No problems with the buttons either, i just gave it a whirl to make sure.
Still it works fine. I'd let it go for cheap. The only thing I don't have is the AC Adapter. I do have the original box though.