This is for a german forum, I once registered an account but never saw the need to use the account, it seems to be a waste of time for me, I guess it was because of these bots your selling, no one responds to the threads and just open their own selling threads.
It is indeed a german forum, but the general trading section and also the game-specific trading sections are nowadays crowded with also english threads. Just take a look and you will recognize that there are many english speaking users as well.
Second, I don't know what you are selling but the response rate depends of course on what you were trying to sell. I was selling for very long Social Media Services and had many replies (cause there was demand), now I'm trying to sell an online game account and haven't got a reply yet...supply & demand.
Third, in order to ensure maximum response rate, you gotta push your threads regularly, every day! There are so many users who push their threads irregularly resulting in a loss of potential customers.