If the seller bought it for $500 he saw the name and only referenced enough to see Masi's can go for decent dollars, too bad.
I agree, at $500. the bike is worth a risk. The frame sets have had a wide variety of trackable sales prices, from $175. to $400. (400 was way too much)
This frame was forth string in the Masi USA lineup, third as the Gran Criterium was kind of on close out at the time.
I do like this frame more than the Nuova Strada just above it for whatever that is worth.
I would assume as others do that the bike will need mechanical attention, and the tires are probably suspect. Hard to tell but it may have Fir rims, a good thing.