How to check what product can sell and what product cannot sell in Ebay? Just wonder, shall we test water first before order the product in bulk? Any advice?
You can use the API to "find popular items" etc... http://developer.ebay.com/DevZone/javascript/docs/JSDocs/logical/FindPopularItemsRequestType.html
If you want to check demand for product you can always check the number of product sold also it is always advisable to check for feedback. Auction listing is another way to check for product which are in demand. Sellers sale high demand product on auction listing.
The best way to find out is to sell a couple in auction first and see what feedback is received before ordering bulk.
The best way is the "Completed Listings Search." This shows all the listings on eBay that have ended on eBay from the previous 15 days. You can get there, from clicking the "Advanced Search" link. Hope this helped!
Just type in ebay pulse in search engine. Checking completed listing is another great tool as mentioned above.