You don't need to trust anybody to see the order book that information is public, and you just need to know the issuer address. You only need to trust them to receive the IOU's they issue, which is more or less a prerequisite to trading them. (This is important, because trusting two gateways without setting any other options amounts to agreeing to serve as a free liquidity provider, which may not be your intention.)
For reference, WeExchange's issuer address is rpvfJ4mR6QQAeogpXEKnuyGBx8mYCSnYZi. (And if you're interested in the fuzzy line between user and gateway, you can set the issuer to rpH3zuMch2GrrYX724xGWwbMGwiQ5RbSAU to see the order book for molecular's BTC IOU's. Be sure you understand what you're doing if you buy any.)
Taking a look at the order books for BTC/XRP. So if I want to buy a Bitstamp BTC I've got to pay 68,000 XRP. If I buy molecular's BTC I'm only paying 60,000 XRP. That's the market discount on a non-Bitstamp BTC IOU... for the moment. Not all IOUs are created equal, I guess.