Hammerer:
I'm always evaluating a trader's feedback, the sort of questions they ask and how they sell products. Any time I don't want them to do the same to me then I blacklist them. That way I'm reducing the likelihood that I have to waste my time on them. The blacklist primarily functions to prevent them bidding on your auctions but the list serves as a useful reference I can check when buying.
Spending time blacklisting traders might seem a waste of time given that there are so many traders and their is little likelihood that they will actually be active on one of my auctions. In reality the probability of them interacting with me is much higher than a random selection because I see these bad traders involved in the same subset of auctions that I have bought and sold in.
I have blacklisted a few, and it feels good when you have a buyer who doesn't complete a sale etc. But I have noticed that the blacklist page is impossible to find. I have to do a google search to find it, as I can never find it on the account page.
I ahve actually had more problems this year with traders than any other year since it started. I have given 3 negative feedbacks this year alone, when previously I had only given 1 in all the previous years.