Used Car?

I’m in the market for a used car and looking for some advice. There are so many used cars for sale out there, but I’m not sure where to start. Is it better to buy from a dealership, a private seller, or online platforms?
What should I be looking for when checking out a used car to make sure I’m not getting stuck with a lemon? I’ve heard things like checking the car’s history report and having a mechanic inspect it, but is there anything else I should be doing?
Any tips would be helpful.

There is honestly dozens of things that you could check in a car. I could list a few important ones:

• Check under the car for leaks
• Open the oil cap in the engine to check the state of the oil (if it looks muddy, there's probably a big issue of refrigerant mixing with the oil, definitely don't buy this car)
• Check if there any smoke coming out of the exhaust (blue smoke means the car is burning lots of oil, white smoke means it's burning refrigerant, black smoke usually indicates a rich AFR)
• Drive the car and check for strange noises or excessive vibration
• Check that all the gears go in when parked, check all the gears when riding.
• When driving, try taking sharp turns in both directions and check for unusual noises.

If you can lift the car:

• Check there are no visible oil or refrigerant leaks (if parts under the car are wet and oily, probably means there is a leak)
• Check for play in the wheels. This could indicate bad bearings, bad ball joints, bad tie rods.

Inside the car:

• Check for wear in the upholstery and the seatbelts. Excessive wear on this components may indicate the car has more miles than advertised.

Outside the car:

• Check the paint in all the panels match. If they don't, there's probably been a crash.

When under the car, try to see if you can see differences between the left and right side. If one side has all new components and the other side has much older components, it could mean there was a crash on one side and some things were replaced.

There is probably more things to check, but this should give you a good idea of the state of the car.