I see the list of items in the arms/armour vendor, with prices for every item.

As I click on one item that I want to buy, it goes in the bottom of the window but with a totally differnt price.

 

Is a bug or something I don't understand?

 

The differnce of the price is huge. A spear marked 150cp gets to 4950cp!!!!

I've had this happen as well. Suddenly when I got out of vendor screen to check my equipment and see what I'd need, upon returning to the merchant I was just unable to buy even a single piece of gear, most stuff jumped up to 4950 like you said

Edited August 20, 201411 yr by Nordicus

I had the same issue..... Strange.

I looked into it further, and the issue is that it seems the prices are right, but the initially shown items are possibly from a wrong table, showing regular, unenchanted items rather than the proper upgraded ones.

 

On the left you see a simple, basic dagger, on the right after you've clicked on the item in order to trade, you see the actual Fine Dagger with 2 enchantments

Edited August 21, 201411 yr by Nordicus

I had this issue as well. I thought it was false advertising or possibly a missing negotiation skill.