Dear friend buying a car in Doha especial y if it used is a Farley simple process, I have done so many times and it does not get easier

Now finding the right car for you will need a little time searching the net you do not need to physically search as almost all privet sellers and showrooms are on the net through the following websites

Qatar living/qatar sale/carsemsar

Find the car
Go see it
Liked it
Check it
Pay the money and transfer
Congradulations your new car

Take the car to the check up I usually take it to the German center for check up they are good it coasts around QR.300 for a full check up including paint check

You have two choices of buying a used car, you can either buy it from a used dealer shop or directly from a seller. You can search the net for both but buying from a privet person selling is much easier cause the paper transfer of ownership is direct between you and the seller as if you buy it from a dealer you have to pay the dealer around QR.1,000 to finalize the transfer process for you and you have to wait for the car until the transfer is done.
If you buy from a privet seller and after liking and inspecting the car you go with the seller to traffic department both of you fill the necessary documents there where the car plate number will be automatically checked for fines before transfer . There is a QR.300 transfer usually paid by the seller.

hope this helps you and good luck