When bidding in auctions that don't accept currency, the value of your bid is determined by an 'estimated price'. I got a Hawk-Eyed Hunter cosmetic that I bought for 3.6 ref from Scrap.tf, but it's estimated worth is 2.55 ref. That's a relatively large jump.
Comment below if you think the current system is fine, or needs to be somewhat closer to Backpack.tf prices.