>>1806751it had a kickstand clamped there, which is pretty common and also commonly damages frames.
probably just rubbed the paint of though, but you'd want to have a closer look seeing as it's an aluminium frame. If it's dented i'd pass. A dented steel frame is less of a big deal.
I'd pass on it. Cromoly steel old mtbs are much more desirable. Plus the build is junk, heavy steel post and stem, gripshift, plastic brake levers.
It's just not quite good enough.
