Hi. Having bought a second hand car myself a few months ago I think there are basically 3 options.
1) go to the dealers that sell new cars who also sell used vehicles. You should be able to get a recent model that has been reasonably well inspected, may even have service records and may come with some sort of conditional warranty. This option may not be the cheapest option but might provide the most peace of mind and may in the long run prove to be the most cost effective.
2) go to any of the seemingly hundreds of used car yards and take a gamble. Many of them are clustered in one area of Dubai. See if you can get a private inspection of the car. You might find you have more time to reach a deal with these guys.
3) find a car for private sale through Dubizzle (or other sources e.g. Notice boards, word of mouth etc). And have the vehicle checked thoroughly by a reputable garage. This is not so easy. The seller has to be willing, you have to find the garage, and you will spend a lot of time perhaps using public transport getting to sellers only to find that the car details were not quite what had been advertised. Bear in mind that Dubai is very spread out so a suitable garage in one area of the city may not be convenient for a car located 15 Kms away. And the inspection will not be free but certainly worth it when you find a car that has good potential. In my view don't accept the mandatory government inspection as evidence that the car is in good condition (but it is needed for the transfer). They really only provide a basic assessment - better than nothing I guess. In my case they failed to note a leaking shock absorber in both inspections. And unfortunately after 1000 klms I've now had to rebuild the auto transmission for nearly AED11000. Whether or not a good garage would have spotted the problem I don't know. And if the major service is due for the timing belt etc (e.g. 100K klms) you can add upwards of several thousand AED to the purchase price. So finding a car with reliable service records in which the key maintenance jobs have been done and on time is critical but will prove a real challenge. Most owners I dealt with were happy to save their AED and simply have the oil changed at the local garage. They were also looking for a quick sale, weren't flexible and exerted a lot of pressure. In some cases it wasn't clear who I was dealing with (it's my wife's car, I'm selling it for a friend etc).
In hindsight I think I would go for option 1 and just accept that I am going to pay a premium price for the used car and hope that the dealer is honourable. You will read many replies that contain less than favourable experiences with the dealers.
Hope this helps.
if a dealer makes you feel better, go for it, but do not trust them blindly. They buy and sell for a living, in high volume, the quality of cars is not better than from the private seller.Thanks my dear, I will go for option 1 as other friends suggested the same.