Seems like venders are a little bugged. A few don't have wares at all and their gold keeps disappearing...
First, I bought a bunch of skill books from Arhu(wizard guy in first town), he had about 9k gold. I sold him a bunch of paintings and gold plates to make it back then switched to another character and his gold went down to like 500. It wasn't due to what I sold him, I only recovered maybe 5k.
Then some random person on the zombie map; he had 100 gold, I cycled through all my characters repairing equipment and instead of gain gold, he dropped to 24 gold. This actually happened as soon as I switched characters and he never gained gold when I paid for repairs.
Seems to happen when I switch characters while in the conversation menu.