Dirty or ill-achieved success is the success which comes through illegal or morally unsound means.
People do unscrupulous things to amass wealth, win a competition, succeed in business or win an election. This is not correct; and not advisable. The consequence is usually devastating.
Clean money is good; dirty money is bad. Clean victory is good; dirty victory is bad. Clean winning is good; dirty winning is bad.
To avoid paying dearly later stay clear of using foul means to achieve, acquire or win anything.