At all cost avoid Philippean Motors in the Automart! Please. They claim to be friends of Emirates but will quite happily sell you a bag of spanners, with 'full service history, one lady driver, never driven in the desert' honest! Then keep your deposit when AAA garage identify it's faults. (AAA garage are awesome by the way)
Stick to main dealers or Dubizzle with a full vehicle check by someone like AAA garage (around 300 AED)
Good luck. If it's too good to be true.......
If you're really brave try Golden Bell auctions,
Gold Bell Auction