Your grandmother probably told you "first things first". Your teacher or first good boss probably advised you to do your homework thoroughly.
Buying a car is much the same way. Do your homework first. Don't go searching for a car loan - even if your credit is bad before you sign on the dotted line. A signature at the bank or credit union - or life insurance policy is always too quick. It is you, not the lender or car salesman who is going to have the headache and cost of the vehicle or payment schedule not the salesman, bank clerk or life insurance salesperson.
First of all is it the car you want - not one sluffed on you. Remember it is your purchase - stand your ground.
If it is a family car don't get pushed into a two door car rather than a more family friendly 4 door. Perhaps even a S.U.V. or a van might be a better choice for a family vehicle. Perhaps even the color is not of your choice or perhaps the color even grates you - reminds you of the color of auto that your father always bought and you never liked. There are plenty of fish in the sea and plenty of other cars and similar cars on other car lots or in the classified ads in your local newspapers or even on eBay.
Next does the car fit the sales description, the registration? Is the data on the sales sheet accurate? Does the mileage match the odometer, is it the original odometer or has the odometer been replaced? Are there tell tale signs of greater mileage than reported on the odometer. Some tips to look for. Have the keys jangled around the lock cutting scrapes in the paint - this is a frequent tell tale of fleet driven cars - such as delivery vehicles or couriers. Is the floor mat worn where the heel of a shoe has worn the driver's floor matt?
Next do a title search. A "Title search" will determine if the car was ever in a major accident or "written off". It amazes people how far a damaged car can travel geographically. Cars that were flooded, written off for salvage value after hurricane Katrina are still showing up as cars appearing perfectly fine and well as far as away as Alaska and Edmonton or Vancouver Canada. A simple title search will turn up the history of the car and if there is significant history that should deter you from purchasing that vehicle.
Check to see if the registration of the car identifies it as being commercially. There is nothing wrong with this. It is just good to know. A fleet car should have much more mileage on average than a run of the mill residentially used car. If not ask why. Or is the mileage not accurate? Again a fleet car is not necessarily bad. It all depends.
If the car was primarily used for expressway or freeway driving then extreme mileage may not be such an issue. That is as long as the car was maintained well and tires are in good condition. If the car was driven in stop and go conditions - either as a taxi or a police or local delivery vehicle that is hard wear on a car and its engine and is not a good thing for you as long as you want a low maintenance , reliable vehicle.
In the end remember that you are on the hook for the any charges and payments. . Does your homework well before you agree to anything. . Do your homework before you sign and documents. It is your signature on the bottom of the legal documents not theirs.