@kathieskorner I'm a small seller (about 700 listings) of single quantity, long tail items, mostly used and vintage. I understand the "logic" you are talking about, and I think I can safely say, based on my experience and the experiments of other sellers (with similar inventory) , the logic does not apply in real life.....is is fine for math, but meaningless when it comes to selling a large variety of long tail items. (I have no experience with multi-quantity, newer items).
The logic might apply if you are selling in a fairly tight niche, and maybe it does apply to the OP, I can't say.
You are absolutely right that anytime a seller decides to increase listings, he must look at a range of factors (this is a partial list): cost of acquisition, storage costs, even the ability to ship more stuff if sales do increase: shipping supplies must be kept on hand, and of course there are only so many hours in a day---if sales increase and time devoted to shipping increases, will there be enough time to do all the additional listings?
As many businesses have learned through the years, growth may be a goal, but growth must be approached with care.
As I said above, each seller will have to figure out what works to increase sales. For some sellers, increasing listings might do it. For others, maintaining listing numbers but changing the inventory mix might do it. To me, the important thing about the OP's post is not simply "list more", it is the OPs recognition that , if his sales slowed down and he wants to increase them, he needs to look for a solution.
