I’ve sold thousands of dollars worth of stuff (low volume, high prices) on eBay over the decades, and still do on occasion. I’m about to list an iPhone 14 there.
It’s good for high-value electronics and other things where trust is important: Both for my buyers, who know that I have perfect feedback, and for me as seller, because there is a dispute process. I’ve never had an issue there either as a buyer or seller (but I’m not a high-volume seller, just a home user). The peace of mind is worth eBay’s cut… I’m not doing this as a business, just to get rid of stuff I don’t want anymore.
To gauge prices, filter the results by “completed listings”, within some recent time frame, and filter by the appropriate condition and also exclude any outliers too low or high… try to find an average amount among similar items.
For electronics, I offered a 7 to 14-day or so money-back guarantee, buyer pays return shipping unless item is defective. None of my customers have ever actually returned something, but I would assume that guarantee helped make the sales. I thoroughly cleaned and tested the stuff I sold.
I’ve also sold electronics and other things with a UPC barcode (i.e., something I can easily find the correct listing for) on Amazon: https://sellercentral.amazon.com/. You can choose to either handle shipping yourself, or if you have several items, you can send them all to Amazon in one box and Amazon will re-ship them to customers for you (and handle customer service/returns too). That largely took over my eBay selling, until I discontinued my Amazon account (due to an unrelated issue — their treatment of warehouse workers).
I also sell the occasional low to mid value thing on Craigslist, especially items that are too bulky to ship. It’s not a very nice experience (tedious, lots of bots and spam) but of the people I’ve actually met and sold/bought things from in person, I’ve similarly also only had good experiences — across dozens of transactions in many cities & states.
Facebook Marketplace would be the easiest out of any of them, with both local users and some degree of trust (you can see their account, at least). But I’ve only used it a handful of times… deleted my FB account a decade ago and have had to bug friends & family to sell and buy for me there if there’s something I really can’t find or sell on Craigslist or the other options. It’s a very nice sales platform, though, and that’d be my choice if not for my ethical gripes against Meta.