When Someone Post Their Rewards for upgrading their Chop Shop/Weapon Depot Building, Click the Get Yours button. On the “Congratulation” page, REFRESH your page to select the reward you want. After that, all you need to do is to click the “Accept” button and the reward is yours.

There is no big deal about this glitch as the rewards are all low end weapons/vehicles. It you had already collected the whole list of “Common” weapons/vehicles, give others a chance to get theirs.

Mystery Bag Glitch

If some one sends you one, accept it first by using the new envelope icon at the top of the page and open it. Then leave mafia wars and accept it the same bag again from the facebook home page notifications.

Likely, those bugs Works with other random created awards too. Promotion special bonus, for example.
Try It Guys..