Yes research and learning is the main key to sucess. Yo need to try and guess in advance at what your item will go for. But never consider ebay an only option as there are many ways to sell products.
Recently I had a pack buyer complain about some 2 way radios we sent them. Saying they are nice but they are completely worthless on ebay. They sell for around $5.00 profit.
I actually have several hundred units. And ws just using the rest as pack filler items. Maybe somthing usfull for the buyers to play with or sell to a freind or give to their kids..
Me and my cousin sat on my living room floor and put together over 45 of those radio sets that were completely out of package. We tested them and we charged them all up and put the individuall sets in small garbage bags.
My cousin took them to the factory he works at and sold every single set in 2 days for $25.00 to his co-workers. He earned $5.00 from me for each unit he sold. So it 2 days he turned 45 units into $900 profit for me and $225 for him on items that you dont get more then $5.00 for on ebay.
So the moral of this story is stop relying on good ole ebay when you have so many ways you can sell items for more anywhere else. Yes ebay is a good place to sell items but if you research propertly you can make money literally anywhere.
I dont just sell on ebay , I sell on ebay,amazon, our websites ,to our freinds and family, yard sales,flea markets, and Local Public Auction Houses. And our local newspaper has free classifieds for items under $99 we list there every day. There is not a single item we dont profit on. Even if the item is damaged we can still sell it for money or scrap.