Does it work like this?

I am an expert at 3D printing, but it’s not what I do for a living. I was at the library the other day, making copies for my own business. That part doesn’t really matter. What matters is that I noticed that the library had a little 3d printing lab, with one shitty 3d printer. I have 4 printers. I want to donate a good one. If I donate it, is it a write off/ exemption. Or is it a credit. What I mean is does the value of the machine that I’m donating count for its value or should I sell it on Craigslist?