This is really smart. I feel like it further establishes SeatGeek as the inarguably best destination to buy tickets: peer-to-peer at lowest fees in the industry, combined with the best prices on the web.
If you consider a marketplace to be (demand side) : (supply side), they already have a backstop in the supply side through price-comparison, and can now differentiate their service from other companies with a solid user-uploaded set of tickets.