Sayulita can correct me if I'm wrong, but I believe that each seller can set their own profit target - that 10% figure. The 2% is what sayulita charges for the matchmaking. In the past, I've frequently bought and sold bitcoins at 0% profit margin, and the most I remember paying is just 1-2% on top of the BB fee. It all depends on what the seller is asking for. If you don't like the price, you can ask if there's another seller (perhaps at another bank) with a lower fee.

It's not that different from localbitcoins.com. Each seller there (or buyer!) can set their target price to whatever they like, even double the benchmark rate if they so choose.