Well, a build is not a hard thing to fix, just go over it. If it was converted to a FTE, no big deal, as long as it was a total transformation.
I have no problem buying used rides from trusted racers, its a great way to get into a class w/o spending a ton.
The $300 for the Jammin is actually a bit high, depending on what all is with it. These buggys just dont seem to hold a resale value. I had my FTE roller on sale here for $210(but just regular Ofna shocks) and it took forever to sell. I have also see other FTE rollers for around the $200 mark. Spare parts are great, but they are CHEAP for the Jammin. Just double check the outdrives they tend to wear, but mine were fine. I have seen the servo plate crack on these as well, you can double it up or get a alum. piece.(thats what I did)
Is the SP2 stock? Usually as Jet said, they need a few hop-ups to make them what they need to be. Mostly people us King Headz parts, which are not the cheapest, but are of very good quality. As for spares, K stuff used to be a bit spendy, but check around. What box is he including? How worn is the wheel(but they are cheap) and does it include a battery?
As for driving the buggys, it REALLY is subjective. Driving someone else's set up may turn you off to a buggy because he may like it one way, and have it set up for his driving style.Different servos,mills, and clutch set ups can turn you off to a buggy when it could actually be tuned to what you like driving style wise. That is what is so great about these things, they are SOOO tuneable. If your just starting out, you may be "numb" to set up changes anyway until you get the real hang of racing. Heck,I'M still numb to a lot of it!!!
Here is a bit of a cheaper price, but they are out of stock too. Both AMain and Carolina have codes to save $$$
http://www.carolinasrc.com/webstore/Scripts/prodView.asp?idproduct=2635