Hi! Welcome to RCTALK.COM!
This forum is dedicated to all sort of r/c!
There are ppl doing on road and off, bashingv crawling etc.
I just bought my "first" on road car too.
Mine is an old Kyosho.
I doubt it will win many races but I really like the car and I'm going to run it anyways.
I have lots to learn too!
New batteries can cut lap times for sure! Batteries are at their best when they are new. Plus if they weigh less or helped to balance the car better, lap times can and do go down.
Used gear is tricky.
There is a classified section here on the forum.
https://www.rctalk.com/forum/forums/for-sale-trade/
I recently bought a couple motors and an esc from a member here and I'm very happy.
You can look there.
Buying used gear can work out OR you can be buying from a shady seller who knows the gear is about to give out, or a seller who simply doesn't know the history.
Buy from a reputable source!
use paypal AND a credit card if you buy from ebay. That offers 2 layers of protection against fraud if you happen to get unlucky.
There is a 3rd option though...
There are "kit breakers" who take apart new r/c's and sell the parts, cheaper than factory.
Jennysrc.com is one I've had good luck with. Lots of ppl buy from them here.
I'm sure someone here can help you with your specific kit and offer more info that this too.
You might want to ask around that track to see if anyone is selling their car.
Its a common thing for a racer to sell to "upgrade" or change brands, cars for a number of reasons that don't include "I'm selling it because it got ran over"!!!
Look for a car that looks like its in good shape, is clean and well maintained.
Look at the bottom of the car!
The "pan" will show you a history of the car.
Some light scratches are to be expected.
Lots of heavy scratching would indicate outdoor use to me. Not always a problem but dirt causes wear. Carpet doesn't have dirt.
It could also just mean that it was run on an asphalt track... use your judgement.
If it looks like there are any "pin or puncture "dents", pass! They have been running the car off of jumps!

A well maintained car is less likely to have hidden "surprises" like I keep finding on my ebay bought optima mid.
2 final thoughts... a factory car with no upgrades would indicate a car that hasn't been raced much competitively, not as banged up.
A fully modified car at the "right price" could save you a LOT of money in carbon fiber and alloy goodies.
Do research on the car. Make a list of "extras" that you'd like on your car. Use that list to help you decide what you will pay.
Hopefully you have more than a few cars to pick from and you find whats best for you!