30k price or 30k miles? 30k price way too high that's more than it sold new (in the usa where I am anyways) 30k miles depends on price maintenance history and condition of the car. I have a similar 2011 s GT hatch fully loaded to the hilt 61k on the clock when I bought it, other than the dealer putting cheap crappy firestone tires on it its been fine. had a couple of minor issues one the dealer assisted with fixing the other I fixed on my own (dealer fixed leaking headlight assembly caused by bad ballast seal, expensive! over a $1000 in parts, could not tell this car had this issue until 3 days after purchase when it rained hard and got a bunch in, long story about the fix but it got there) and right rear caliper seized on me, but again I am mechanically inclined and maintain my cars myself for the most part so swapping a caliper and bleeding the brakes is no problem with a few tools and a friend to pump the pedal for you. look over the motor mounts or have a shop look at them before buying (have a shop do a full inspection anyways always a good idea on a used car) as the passenger one under the coolant tank fails regularly, usually noticeable by really soft rubber that just "deflates" would be the best term when you touch it or fluid leakage around the mount (its a fluid filled mount)
if its an auto transmission check the color smell and fill level on the dipstick of the fluid after driving it for about 5 miles should be clearish red to very light red and have no burnt smell to it a white paper towel helps to identify the color on this fluid better, same for level putting the dipstick against a white towel helps make the fill level easier to see. if its at 30k miles if it has the oe tires they are probably shot and are too old anyway (age wise, rubber rots in about 6 years or so especially tires as they get hot and just sit out in the open all the time) and will need to be changed, check the date codes on the tires, each tire company has different date codes so just google tire name date code and it will tell you how to find it. Check the lights and everything electrical for full functionality all the windows door locks mirrors sunroof etc. don't wanna buy it, get home and find the sunroof wont open or the right rear window wont go back up after you roll it down. check the leather seats are soft and don't have a bunch of cracks or creases in them (leather will get a few wrinkles with use and age so don't worry about a few especially in corners. have the shop scan the obd2 port to make sure check engine codes are not present or recently erased (don't wanna drop big bucks on a car and deal with a $600 catalytic converter issue right away) that's really about all, if your in the usa nadaguides.com and kbb.com are your friend for making sure you get a fair price, use them.
Inspect the car thoroughly, look at any carfax/autocheck report you can, but don't count on it alone to uncover any issues as they don't know a lot (I had a sentra when I was younger and stupider that showed no wrecks on carfax) later needed something near the front bumper went under to look and as I reached up to get at it a massive triangular dent in the subframe bumper area, looked like a pole impact, would not have know from looking at or driving the car so very detailed inspection is key and a shop that has no vested interest that you trust is best, I had been under that sentra and did not see that huge dent because the splash shield blocked it so lesson learned, a bad Toyota celica taught me to buy an obd2 reader and check code history before buying
as you can see below in my signature I have been getting about 26mpg in the car (us gallons and measured distance in miles) which is a little above rated for this car. as I got used to its particular driving quirks or basically figuring out how to make it get better mpg I can share a little with you and anyone else interested. I have an automatic (wish it was a stick, could not find one oh well) if you do get auto and know stick use manual shift mode, you shift more economically then the car does usually. I drive a lot more highway then I used to (got a new job same day as the car ironically) seafoam helps keep the engne really clean this helps its be efficient run it through about 2-3x between oil changes (more if you do longer intervals less for shorter ones) easy on the fun pedal is a no duh but one im going to state, the car is fun but fun pedal down=no gas lol. coast when you can, but if auto leave it in drive when you do, its harder on the transmission to shift from drive to neutral a lot. use the manual mode to engine brake a little, saves wear on the brake system and I noticed it seems to help my mpg just slightly which is almost counterintuitive. and don't idle forever for no reason, shut it off if your going to be there for 10 minutes or more. cars get 0.00mpg when idling so its just wasting black gold. and use the current mpg setting on the info screen when you can, the average one is not very accurate (I don't know that the current one is either, but it helps me drive more economically seeing it drop)