Wheeler-Dealer is an achievement/trophy in Metro 2033 and Metro 2033 Redux, awarded for exchanging 500 Military Grade Rounds at exchange kiosks. You can both buy or sell the MGRs, so this is not difficult to achieve, but all 500 must be exchanged at once. The best tactic is to wait until you have at least 500 MGRs, then go to a vendor in Polis or Armory and buy as much shotgun ammunition (it is the cheapest) as you can. Sell it back, then rebuy, repeating until you get this. You can always reload a checkpoint to retrieve your MGRs.