The most fundamental and important trick is of course learning how to find the government vehicle auctions, but that's actually pretty easy
. In fact, I know of a website where you can check out the nearest auctions in your area of residence, so you don't have to deal with the hassle of driving across states to find a good deal. Once you actually reach the government vehicle auction you're looking for... well, that's just a matter of having decet bidding skills, and it certainly won't hurt to have some knowledge of car and mechanics.