But this last PT is quite different. I can't buy all the armor I want without scraping every coin and going back and forth to camp to collect sellable stuff that I looted but couldn't carry.
The price is adjusted based on the persuasion score of the character who started the interaction with the vendor. The price is also different based on the difficulty level.
You can also lower the price by offering the vendor gifts to raise their attitude. The amount of gold you need to increase the vendor's attitude toward you is dependent on your level. The higher your level, the more gold you have to offer as a gift.
The highest price possible would be if your character had a charisma of 8 and you were playing initially on Honour Mode difficulty, but then you changed the difficulty to custom and increased the price multiplier from the custom screen. In that case, it would use the base increase for Honour Mode and then raise it even more with the custom multiplier. Playing that way gets costly real quick. Decisions have to be made early on.
*
The exploits are things like selling a vendor a backpack. Then you open the backpack from the vendor's inventory and move all the vendor's items into that backpack. Then you open a backpack from your inventory. Then you slide all of the vendor's items from their backpack into your backpack, but don't slide the stuff into the slots. Instead, slide the stuff onto the picture of the backpack you see at the top of the open backpack.
All of the vendor's items will appear in your backpack for free. Exploit. Everything's basically free.