Can't speak for the OP, but if you ask me, you can always sell a magic item. If you want to offload your
+3 longsword, you can walk into any town and do it. The town guards will happily pay you 25 gp for that nice, well-crafted longsword. When you demonstrate how you can drop a wisp of fleece onto the blade and the razor edge slices it neatly in two, they'll be quite impressed. They'll give you 40 gold for a sword like that, maybe even 50!
The question is what it takes to find a buyer who'll shell out big money for your oh-so-precious-magic-item-that-still-isn't-good-enough-for-you-to-keep-and-use-yourself.
The DMG guidelines are a good starting point, but they aren't the be-all, end-all. If you're in a small town out in the boonies, ain't nobody going to lay out thousands of gold pieces for your magic items. It just won't happen no matter how hot your dice are. Nobody here
has thousands of gold pieces, and if they did, they wouldn't spend them on a sword--they'd buy a house, hire some servants, propose marriage to the mayor's daughter. You need to go to a city if you want a good price, and then other complications arise. Lots of places have strict laws on who's allowed to carry even mundane weapons, let alone magical ones. If the local lord gets wind of what you're up to, she might decide you're a dangerous troublemaker and your magical weapons must be confiscated... for the good of everyone, of course.