Unless a person has lot's of money and can just buy whatever they want shopping for a used car can be a challenge. I went through that a few years ago and about 15 years ago. Here is a couple of websites that might help. Everybody knows about Autotrader.com but, in case you don't it can be helpful.
http://www.autotrader.com/
Also if you zero in on a used car you like you might want to use Carfax. I think there is a small fee to run Carfax for each vehicle but well worth it. You can use it to run a background check on the vehicle to see how many times the Title changed to a new owner, If the vehicle has been involved in a wreck, if it has been in a flood, etc... I was told Carfax is about 80% accurate, not 100%. Carfax has been around for a long time and so has Autotrader.
I used both of these when I bought my last 2 vehicles. Just a couple of pretty reliable resources to help a persons search.
Use Carfax to get a Carfax background report, not shop for a car.
Good luck and be careful.
https://www.carfax.com/