I'm learning more and more everyday but I don't trust myself when it comes to figuring out used unit purchases..

I found this unit and have been talking to the seller: Link with Description here!

I noticed it was built by person X. Lets assume the builder knew his stuff. Does this all sound legit?

the tube inside plays the biggest part of a pvs14 value. that housing is worth about $500 to $600

It's a crap shoot when you buy used. I bought a used Pvs14
Last month.  It has been great so far no black spots.
I have been a  lurker in this forum for some time now.
You have to ask the right questions to individuals that are selling these used home built PVS's.
You can pick them up cheap most of the time.
If you can save up for the TNVC pvs 14 that's what I would do. Warranty versus no warranty.
If not take a chance and buy used.