Car checks get as tricky as compared to a innocent person who has a very simple face and look but the mind is a devils workshop. Most of used car dealers keep the cars perfect from the exterior body line is clean and looks as good as new but the main things to check out is the engine and the wiring as I have come across some cars in uae with chassis being cut and welded from centre. That's 1/2 car body attachment. Also we see a lot of vehicles who's engine has been changed or even gear box so when you take this vehicle for passing the rta guys will ask you to go back to the showroom or service centre of the particular brand and get that verified and need a company stamp on documentation.
I suggest it makes sense in paying 500dhs or whatever charges and get the vehicle checked before buying it. Cause once you have purchased it then you are forced to use it is the same way it is.