Bargain is a General skill. You can change the prices (e.g. lower them with more levels in the Bargain skill). Also, having a high Honor stat helps a lot. Whenever you put skill points into Honor, your Influence will go up (IIRC) You will find info on the General skills
here, and info on the stats, both normal and derived,
here. Also, the slider bar you see when buying items is the "change amount" slider bar. It has nothing to do with bargaining. Hope this helps!
