JVC projectors are no good at 3D old or new, so that isn't a consideration. Presumably you are looking for a 2D only machine. The most recent JVCs are presumably better than the older ones - but not much better. The black level superiority of the JVCs seems to have been there from the start.
So while many projectors should probably never be bought used, the JVC LCoS machines may be an exception. The very first of these JVCs is likely to still produce better blacks that even brand new DLPs.
Used DLP machines are bad buys because they have two moving parts - the fan which all projectors have, and the color wheel which are only in DLPs. Both of these spin and so both can develop bad bearings. This makes the likelihood of a squeaky bearing double for a DLP. But three panel machines can get out of alignment and become fuzzy.
The most important issue would seem to be the "right of return". Can you get your money back if it doesn't perform properly?
I presume you have counted on having to buy a new bulb. So a used $1K machine will actually cost around $1.3K.