Ahh the question with racing karts for sale, should I buy new or used? It's asked before buying anything.
As with buying anything new or used, try multiple places, and research a little bit.
It can make the difference between getting good quality and bad.
Some advantages of buying new is that everything is top notch and usually the newest thing out. You won't be outdated in a New Kart.
Buying a Used Karts is a little bit trickier. Yes you can save money, but it's also riskier.
For some indoor kart racing, you can use a Rental Kart(Coming soon) to race. Don't discount it because you don't own it, a lot of people still have a lot of fun doing that and they have leagues and everything.
My first kart was a very old used kart. Even though my competition had better karts than me, my dad and I worked hard to learn everything we could and we eventually started winning with this kart.
It doesn't hurt to start out with less than stellar stuff, it can really teach you how to win with ability and know how alone before you get into the top of the line stuff.
So remember, yes equipment is important, but so is dedication. I beat many people in my day that very obviously put more money into it than I. Money is important, but being smart and practicing hard is too.
"You'll see the guys, the ones with all the fancy gadgets and fresh new bodies every week without a scratch. What they don't realize is that you can't buy your win, you have to know what to do with that equipment to actually win."
- Tom Trebreh, 2001
The quote above was by a good friend. He taught me at a young age everything I needed to know. Hopefully you have someone that is dedicated enough to help you like he helped me.