"Mint" is a completely overused and hence meaningless term. There are sellers who have a definition of mint that includes copious amounts of rust.

$600 is overpriced. For that price, I'd expect Campy and bling, or at least a 720 with Canti mounts. Maybe 400 tops on the 520, and it would need to be the right size and very clean. You might be able to get six on an ebay sale with some spectacular luck, but if this is a local sale, the price needs to go down.

Pics are really needed here.