There has to be a reason why you are selling less items. I used to look around and do searches for items similar to my popular items when they slowed down. Now i don't wait and search more often. I even use some saved searches with dollar ranges, etc to see new listings. I still have some days where nothing sells. Even over the past 90 days I may go 2-3 days with no sales, but they have been about the strongest 3 months I have had in many years. I am not trying to rub it in, but I see a lot of posts about people complaining about sales. You really need to look around and find new items, new strategies, update listings, etc to build business.
I am often annoyed by changes ebay makes. I have always had good descriptions and listed condition, product details, etc. Then when they made it mandatory I got mad because I hated the time it would take to update my listings to use their item details since they didn't port my details like manufacturer name or part number over to their fields. My sales suffered. Then I gave in. I also studied how to do best in the 'best match' sort I despise as I use lowest price to highest when searching for items. I may not buy the cheapest, but I want to see the range and what is different. To improve my ranking, I got better at loading my tracking on time, getting my packages out on time (still just 75% on time) and making my handling 1 day. When I buy on ebay I don't care how fast it comes within reason and I don't think my buyers did either, but ebay will penalize you for long handling times, etc. I made other changes also. These changes should make a difference. Update your titles. Maybe add words related to how the rocks/minerals/precious stones you sell can be used such as custom jewelry, costume jewelry, etc. Maybe try a markdown sale. Even just 5%. If you have watchers, that may trigger ebay to send them emails noting the lowered prices.
I also began using Promoted (sponsored) listings. It have raised my sales 50%. That's about $1200 per month at a cost of about $60. That's 5% but because its raising sales, monthly store fees are already paid and therefore my overall fee percentage goes down, meaning my profit per item is not dropping.
Good luck. I may even buy something from you. I like the Jade. I'm trying to inspire my daughter to use her art talent to try new things and build her own business. This might be a good thing for her to try.
