Buying used vs new?

Agree with everything said.  There is a small risk finding/buying gently used, but I have had great luck with trade in's.  Someone always wants the next best (more expensive) thing, no mater how good their trade in is.  So, I pick up last year's model, etc., for peanuts.

As long as you are not reflexively jumping at a bargain, i.e., it is a model you want apart from the cheap price, you should go for the deal.  Something like a preamp should last a lifetime and will not be  significantly degraded in performance--it will be like new.  This not like a CD player or a phono cartridge which will wear out and have a limited useful life (in which case you are buying the remaining life of the item without knowing how much use was made of it).

I have put together two systems buying almost everything on the used market. I agree with everyone else. 

If the seller has good feedback I would do it without worry. You'll save a lot of money and get what you wanted for less.