1) It occurs on logout because the underlying mechanism tries to account both for the consistency and value of your successful commerce interactions. It also penalizes you for trying to earn CXP (Commerce eXPerience) through "tricks" that don't make good business sense.

2) It's a combination of several factors. If you know how bank credit ratings work, it's somewhat similar. Just like in real life, merchants (and banks) will trust regular, consistent suppliers more than someone who sold them one huge item then vanished. Also, you learn more about business acumen from negotiating lots of intermediate sales, than you do from brokering a single large one. That said, all other things equal, you're better off doing bigger deals than smaller ones. The calculations involved are also sublinear- doubling the value or number of transactions will generally less than double the eventual reward received. Finally, some transactions aren't worth squat- Jimbob the Kingpin of Galadon just isn't going to learn anything negotiating for a berry pie, no matter how tasty the description looks.

3) (Not that you asked.) It's not something from which we expect people to derive a large percentage of their experience. Much like exploration, it's a small reward to favor certain kinds of characters who aren't maximally focused on combat. Also much like exploration, if we like how the system works in practice, we will likely increase the reward rate a little as time goes by.

valguarnera@carrionfields.com