I've bought and sold on eBay for more than ten years. If you want to sell something online, it doesn't get any better than eBay. I like to think of it as an online garage sale. The advantage of selling on eBay over having a garage sale is exposure. Instead of having random people from a limited local area looking at what you are trying to sell, you get a nationwide, or worldwide, audience. And your auction listing will also get a targeted audience. For the most part, the people looking at the item you list are people who are interested in exactly what you are trying to sell. They had to search for your auction to find it. With a targeted nationwide audience, that item that you would be lucky to sell for $10 at a garge sale might now find buyers willing to pay many times more. You can make a greater profit when selling on eBay compared to selling through other common venues.
As a buyer, sometimes eBay is the only place you would be able to find stuff. If you're looking for used, vintage, antique, collectable, rare, unique, one-of-a-kind items, eBay is still the best place on the internet to find them. Over the years, eBay has evolved into a marketing tool for sellers offering brand new products, and sometimes you can find good deals on those items too.
I love eBay.