Each bid costs $0.60. You can only raise the price by $0.10 for each bid. If a $150 GC sells for $40, then that means 400 bids were placed. They made $240 off just that one GC. So even if other GCs aren't selling for that much, they make up their money on the more popular ones. You end up spending more money too than just the $40 you paid for the GC depending on how many bids you placed.
I don't really like their bidding system because each time you bid, that adds 20 seconds to the clock. This means you could be sitting at the auction for FOREVER! The end times are never really when the auction ends unless no one else bids. It's a good deal for the GCs that aren't as popular though.