iRock

I am in the market to buy a car and seen few cars of different brand and age as per my assigned budget, but I am highly curious to know how do I actually find out if car odomoter has been tampered or not? Some car look really beaten twice for the odometer kms and there is no way I can challenge the owner. I know some people use it rough than others, but difference is huge and noticeable that leave me no option but just to quietly walk away from those rotten deals.