Pinterest was originally not meant to be for self-promotion.
I pin an item from my shop every week or two at most. I have a "shameless promotion" board but lately I've been pinning my items on random boards to blend in with the rest of my pins. I use Pinterest mainly for entertainment to get ideas, collect recipes, quotes, etc. I get a tiny bit of traffic from there but nothing to get excited about. I think most people use it for ideas so fair warning that you may see your items repinned onto "DIY" boards. It's the nature of the website.