I used to sell on eBay. I lived in an area where I was able to find lots of brand new, clearanced, overstocked items at the end of a selling season. (The stores had to make room for the new, incoming models.) Or items that just didn't sell well in that area.
For instance, I found about 25 NOAA emergency weather alert radios. Normal price was about $60. I got them on clearance for about $15 each. They sold on eBay for $30.
I had no idea at the time what those weather radios were for or why someone would need them. Then I noticed most of the addresses I was sending the radios to were places like marinas, tornado regions, hurricane areas, etc. Since where I lived, we had none of those and had no need for NOAA radios, they didn't sell here. But, people who needed them liked nabbing a new one half price on eBay.
The hardest and worst things to sell is extremely popular electronic devices like cellphones. The chance for fraud is great. I sold a brand new electronic gadget. I think it was an electronic PDA, when those were really popular. I get a complaint from the Buyer, saying it didn't work and threatening to destroy my 100% positive feedback rating if I didn't take back the item.
I get the item back, and I'm almost positive it's NOT the same, brand new item. It looked like a USED piece of crap. I suspected he exchanged his used item for my new one. But, I hadn't written down or taken a snapshot of the serial number of the item before shipping it out, as that meant breaking the seal on the box and rendering it an open, unsealed item - different from my "sealed, in the box" item.
Back then, I was so new to eBay, that I didn't know threatening a Seller with bad feedback is considered extortion and I could report HIM. It was the days before I had a cellphone camera or digital camera, so I couldn't take a digital photo to send to eBay to show I didn't get a brand new looking item back. So I just took the financial loss and gave him a refund, meanwhile I'm sure he was using the new PDA I had sent him.
Other times, for the popular electronic items, buyers will place a phony bid, just to reveal what the current highest bidder's top bid will be. Then retract their bid to place a bid on different auctions for the same item that they know they have a chance of winning. It would confuse the highest bidders on my auctions to think they were outbid, then see later, no, they are the highest bidders again. Meanwhile, in the interim, they had put in a bid on an other auction, when they thought they had been outbid. If they then retracted their bid, then the next highest bidder (third down) would then be the top bid, and it just caused a mess of problems, as they too, thought they had been long ago outbid.
After that, I stuck to housewares and not as popular items which draws the electronic gadget freaks and the accompanying potential for fraud. But, I eventually moved and my sources for items dried up.