I did try to bribe the traders and get on their good side, but they always had

1. goods I didn't want

2. not enough money to buy my stuff

3. bad prices

Yeah, I didn't really enjoy that mechanic where you get on their good side, don't like it in real life either and I think that's what stopped me from maxing those skills.

I did, however, find a scamp in Caldera who would buy anything with a fixed original price and didn't require any flattery. He also had 5000 gold and when you maxed it out, you just waited for 24h