Hi,
The STR (sell through rate) is below 2% for most of us. This is the fact.
That means - if you have 100 domains listed on the marketplace for a complete year - then, you'll be most probably selling either 0, 1 or 2 domains in a year. (Considering they are good .coms)
If you wish to sell something to the end-user in every 2 weeks then you need a bigger domain portfolio, by calculation you need 100*52/2 = 2600 .com domains at least.