muddiver:
...
nereas must be a manufacturer and wants to keep new product moving.
You must not have read my bio. I have nothing to do with manufacturing.
I was burned by buying someone's used manifold once. It had a stress leak and was not worth repairing. Every since, I have been leery of buying used junk for scuba.
Used tanks are not a problem, as long as you visually inspect them and make the sale conditional upon a successful hydro. I would have the tank(s) re-hydro'ed right away to find out.
Used regs are not a problem either, because you can simply have these re-built at a good LDS.
Used backplates are not a problem, as long as you inspect them closely.
Used fins, some types, last forever.
Used weights last forever too.
Anything else is subject to wearing out and eventual breakage. Such gear only lasts about 2 to 3 years total, anyway. A mask would fall into that category. Thus, I see it as a throw-away item.