I think that frame belongs in the aluminum recycling. It's going to crack
I wouldn't buy that! I wouldn't build that frame up if someone gave it to me for free.
I don't know if you're showing me a crash dent of some kind, or the normal chainstay crimp for chainring clearance (not counting the scratch).
If it's clean and near where the chainring passes close, it was probably there all along (can't tell from the photo).
Otherwise, it it's some kind of crash dent, the frame will fail sometime down the road. However it might be very far down the road, so far out that you never get there.
I'd have no qualms about riding it, since chainstay failure rarely has serious consequences beyond inconvenience. Monitor it for cracks in the area, and at the first sign of a crack, replace it. OTOH even if you ignore signs and it cracks clear through, nothing serious is likely to happen. It can even be field repaired well enough to get home.
An ounce of diagnosis is worth a pound of cure.
“Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
Thanks guys - I guess I'll steer clear.