Having "#1" in one's marketplace thread title isn't already allowed for as you've already correctly pointed out, it can be misleading/induce users into believing the service they're buying is the best one ever when it actually isn't. If you see any marketplace threads with "#1" in their titles, report them and it will be removed from them as soon as possible. As a matter of fact, @Hugo Boss and I were discussing this same matter not long ago. What a coincidence.
/Solved & closed.