You can list old gadgets on places like eBay and Craigslist, but I've had the most luck using a website called Swappa, which is popular in my circle of peers who buy and sell gadgets frequently. I like it because I don't have to meet anyone in person, like on Craigslist, and I haven't had problems with scammers like I have on eBay in the past.
Here's how it works: You create a free Swappa account and then choose "Sell on Swappa" on the main page. You can list phones, cameras, laptops, tablets, smartwatches and other wearables, video games, VR headsets and even smart thermostats or an old Echo.
Swappa will tell you the current lowest listed price in either new, mint, good or fair condition and recent prices for similar devices. If you price your gadget within that range, you should be able to sell it.
Take a few pictures (this is required, along with a special number you include in the pictures to confirm it's you), post some information about it and then wait. I sold a Galaxy Note 9 earlier this year in just a few days.
Swappa takes a flat fee out of your sale — it's free if you sell something up to $50 but gradually increases with the sale price. If you sell something for $1,000, Swappa takes a $35 fee. If you sell something for $6,000, Swappa keeps $250. Here are the fees you can expect to pay.