Let’s consider a couple of variants. If you are an independent manufacturer, the choice of products is not a problem as you sell what you produce. Nevertheless, as a rule, you are not (well, actually you may sell some DIY stuff, but this is not the case of real trading via eBay, put selling single items and we are not interested in such sales). So you major problem is to find a reliable source of products. It must be truly reliable, I mean that the goods you are going to sell must always be available to you and thus to you customer. If you are not a reliable seller, the clients are likely to find it out sooner or later and you will be a roaring failure in your business.
What else do you need?
Well, I would say that there are two ways from this time on: to stock products somewhere or make the manufacturer stock them and use only as required. How can this factor affect your business? It is obvious – your stocking the product will inevitably affect its price (you have to pay rent to the warehouse you use). Of course, you can stock them at your own place, but as your business grows bigger, just imagine how jammed it may become. And if you pay the rent you...