Used, seriously, is there any OTHER kind of regulator? Of the 41 (or 43) regulators currently in my personal inventory, exactly three were purchased new. 1) US Divers Conshelf SE in 1985, 2) Nemrod Snark III Silver (double hose) in 1987, and my Christmas present in 2015, an Argonaut Kraken (double hose). So I love to purchase used regulators.
Here is what I would do in this case: First evaluate your own comfort level for purchasing and possibly self-servicing the regulators you were offered. If you are comfortable with both aspects, then buy them, if you are comfortable with purchasing but not servicing them, check with a LDS that you trust to see if they would be willing to service equipment of the brands you are considering. Get their rates for parts and labor (some places charge more if the equipment wasn't purchased there originally, also warranty work like free parts forever usually only applies to the original purchaser who has maintained the recommended service intervals). If you are comfortable following that, then buy away. If you are not comfortable following your LDS review, then don't purchase.
Buying used regulators can be a great source of saving $$$ (unless it becomes an addiction, ask my wife). Properly maintained, you can get 60+ years of service from a regulator. I know because I have several over 60 that I still dive.
