Most people today are familiar with the concept: You have things you don't necessarily need but others are willing to buy, and you can auction off the items on eBay or other online auction sites. Simply gather your goods, create a seller's profile and start selling.
It sounds simple, but it takes some practice to sell successfully. You need to create persuasive and legitimate product pages for the goods you're selling to get buyers interested. It's also important to set reasonable minimum bids to ensure that people will buy. And remember to deliver the kind of customer service that will garner positive feedback ratings and to communicate with buyers to let them know you're reliable. The more positive feedback you receive, the more people will be willing to do business with you. And that, of course, means more money. (EBay takes a 10 percent cut of anything you sell, plus a 30 cent fee for any item listed beyond the 50 free listings you get per month.)
You can be the best garage sale of the 21st century, or you can evolve your eBay side gig into a full-time business if you really try. In fact, many people start off selling unwanted stuff around their house and progress to actually looking for goods, say at thrift stores, to resell. It's all about finding the right niche (maybe antique vases) and then building trust with your regular customers. As with everything online, competition is fierce, and you'll have to fight to survive, but many people make it work.