How many items can you sell before you should pay vendor fees?

No bucks.
Less and less people would post parts up for sale ... creates a board that would die.
I only come here looking for parts or to get rid of parts and I know I am not the only one.

People's garages would stay full and maybe those parts turn up at a swap meet or they end up in the scrap heap because a lot don't want to spend money to make money.

Most parts I assume are posted by people that find a car that is too far gone and are trying to help others get their cars running.

If you don't have the parts source more parts are eliminated and made into Hondas.

I like to believe the most traffic on these boards are help related or part looking.
I disagree. There are parts listings by the same guys, sometimes more than a page long. over and over and over again. they are it for the money, you can tell by the overly high prices on them. I have always been able to beat their prices on ebay, and using paypal, there is a guarantee. I think they should have to pay for entire page listings !