Quote Originally Posted by Jinko View Post
Yes you are correct in some sense that it is up to the player to be competitive but some sellers aren't interested in being competitive they just want to sell their junk for next to nothing (in some cases much lower than the sell to a vendor price) and ruining the market for everyone in the process.
Undercutting is caused by competitiveness. Lack of consumers, too many suppliers causes a competitive market.

Things being sold less than vendor price a lot of times can be influenced by many factors. However, regardless of what reasons made that player sell his/her goods at those prices, you buy them and make a profit off it.