I spent quite a bit of time the past couple of years buying and selling on eBay, CL, estate sales, and regional auction houses.
As a seller, you have to figure out eBay and get your shipping figured out (keep old Amazon boxes, scale, etc.) EBay is great for selling items you really need to get rid of and are relatively easy to ship. I have been selling video game consoles, old cell phones, stereo equipment, and even some clothes. I feel good about selling an old cell phone for $30. Otherwise it is donated or thrown away. I also sort of enjoy reusing old packaging for shipping that would otherwise be thrown away.
I have sold about 150 items on EBay and I don’t think I have any problems. I generally let people return at their cost and that has never happened. I aim to sell at the lowest price for any item that I sell. eBay is definitely pro buyer. Realistically, there is no alternative to eBay.
CL is good for big items that are a pain to ship like furniture or a grill. Name brand items like a Herman Miller chair will sell well on CL. Always talk to people over the phone when using CL. You should be able to determine if they are a wacko!