It's common practice for 2nd hand items to be ~50% of new (or less).
There are a few exceptions of course, for long-life products like test equipment, camera lenses etc..
But in general, once you've bought something you can only expect to get back 50% of what you paid, even if its 1 week old.
(That's not to say there aren't lots of idiots buying 2ndhand things for more than retail.
My empty argon gas cylinder sold for more than a new one with gas, lol)