Buying used vs new?

There’s a lot of considerations between new and used purchases, including warranty and availability for gear support if needed. My systems contain a mix of new and used gear. I was able to pick up my VAC preamp for 55% of new retail buying used. It had only been used for 6 months and there was no way I would find anything new to compete with it in the same price level I paid.

Buying used can be a good option; you said several years but not how many.  5? 10? 40? 50?  I've bought most of my equipment used but I've drawn the line at things made in the 70's and 80's - some parts are not available for certain models, so you might be left scrounging for second hand parts or trying to cobble together your own.  A selling point often touted for older MacIntosh units is that they can be serviced no matter how old they are, but even with those certain parts are not available.

I bought a "part" (actually a pair of parts) that was built in 1939, so I don't know about a maximum age.  The pair of compression drivers are among the best things I've added to my system.  I don't think there is any warranty remaining on it; I suppose that is the downside.

If the seller is reputable and will stand behind the sale, used is fine.

I recently purchased an ARC SP6 pre-amp from a reputable dealer, it had an issue, I had it fixed (not expensive) and they paid for it. 

The pre-amp is wonderful, and I will no longer need a $20,000 pre-amp, so new is not an option for me.  I am VERY happy with my used gear.

Cheers!

Buying used from a dealer? Dont know where product has been. Like meeting a girl or guy. 
How does one know about product history, ie preamp, or does it matter?