I have used seatgeek twice and loved it!
I recently purchased tickets to Bull v. Cavs basketball game using seatgeek. The vendor was ClassicTickets-they charged my credit card. I agreed to pay $569, but there was an additional fee of $27.00 for taxes from ClassicTickets. I called Seatgeek and told them my problem and they happily refunded me the difference of $27.
I also used them to buy tickets for a 76ers game. To my surprise, they gave a $20 food voucher at no additional cost for each ticket.
I love using seatgeek to by ticket!