i think its intended. All skillbook vendors dont generate money anymore so you have to use all the other vendors. I dont have problems selling my stuff and getting money though. My party is lvl 8 and i have about 90k gold, with lots of items still need to be sold.
but the other vendors don't regenerate money either, I already cleaned them out. Why force us to use the other vendors anyway? They sell meat and vegetables why would they want my swords and why would an arrow vendor make no money... if it is as intended it's contrived and pointless... Just wasting my time running back and forth between merchants and limiting my payout.