There a few used SVS subs local to me for sale. There is one PB12/2 Plus and a PB 12Ultra. The last gen models. They are priced between $600-750. Assuming I can audition them prior to purchase is buying a used sub a bad idea overall?
I was looking at getting the new SVS PC12 NSD which would be $600 or so shipped but I'm thinking a used PB12 2 Plus for the same money might be a much better move. Thanks for any views or advice.

No, it is not a bad idea. You can generally get the older gen models for 50-60 cents on the dollar and get very capable subs at a huge savings. Most models like those of SVS are generally very bullet proof and usually require a tremedous amount of negligence and abuse to damage. On top of that, the warranties, if in effect are transferrable as well.

I have and would buy used subs.

I have purchased used AV and pro-audio gear in the past. I guess a lot of the decision would be based on your appetite for risk. There is always a risk when buying used. Being able to audition should help but you can't always tell.

I have a PW2200 that I am not using. This sub sounds great and as never really been worked out hard (family won't allow :D). However, the cabinet is in bad shape with the grill cloth coming out do to a tipped chair, wax on the surface due to careless wife, etc. On the other hand, I have a pair of JBL pro-audio subs that despite heavy use (DJ'ing) the cabs are in near perfect condition. However, I have sonically abused these subs. The moral of the story, is appearances can be deceiving.

I bought almost all of my speakers used this time around... including my sub.

I bought my set of Monitor Audio speakers from Audiogon and my SVS PC-13 Ultra from the AVS classifieds. Worked out for me... just make sure the sellers are active and have positive feedback. Craigslist can be more difficult.

As long as you can check it out thoroughly beforehand, I see no reason to fear used gear. In a hobby like ours people constantly upgrade, lose interest, hit a short money spell, or are told to sell their gear off by the wife. I see no reason not to take advantage of all of that, and have done so many times.

Most things either work or they don't. On a sub you have to be worried about the condition of the surround (foam rotting, etc.) or a loose suspension that might cause early bottoming out. But these are easy enough conditions to verify.