More often than not, being in the wrong circle of friends will be the cause of your downfall. This has everything to do with self-protection. If you don't want to get into trouble, don't even try doing anything that is even slightly illegal. People who deal in the black market, obviously, have no rules to abide but their own. Once you accidentally cross them, you might find some questionable subjects arriving at your door in the middle of the night with some threats or other unpleasant intentions. Stay honest and stay legal; do not try anything dubious, and you will not become a target for any dark forces. 

So maybe you're not as rich as some people. Maybe you're even struggling to pay the bill for your family. But smuggling forbidden artifacts is really not the answer, nor is buying illegal dark objects that supposedly could do some amazing things. Remember, if they sound too good to be true, they probably are. Always deal with everything through legitimate channels. It is never worth it in the end, and even if you get away with it once or twice, do you like having to constantly look over your shoulder in paranoia for the rest of your life?

Another important thing is choosing the right friends. Friends always affect you with their own thoughts and opinions, and it's not impossible that some of them may try to get you involved in dark magic. And once you're in, it'll be hard to get out. Because dark wizards don't appreciate it when you suddenly decide to quit. One thing good about them is they're all devoted to their leader. There is no resignation form to fill if you have made an oath to be a Death Eater.

And once you're in, do you think it's only you that has to bear the responsibility? No, your entire family's fate rests in their hands too. They can threaten to hurt your loved ones anytime, or even punish them for your failures and mistakes. You simply do not want to get close to these people at all. If your friend has started saying things that are even the slightest bit suspicious, better to quickly get away before it's too late. 

Just the same, do not try to convince them to forget their old ways or threaten to report them to the authorities. Of course you must report them, but let's not tell them that, shall we? It's to prevent you dying before you could do so. Forget trying to stop them yourself. Leave all the work to the authorities; it's the safest route to take. Even if they are your own friends, you can never be sure what they would be capable of now. 

All in all, simply be careful with who you're dealing with, and hopefully you will never have to cross path with dark forces during your lifetime.