How do you know if you're a victim of a scam?

I know two people who a playing in two different sweepstakes. One is for Publishers Clearing House and the other in a magazine sweepstakes. The one that is in the PCH drawing had to send no money or anything to enter but the other person that is in the magazine sweepstakes has had to send in money to continue to have their name entered into the drawing and have received notices stating that they have won over 6 million as I write this. The thing is that the person continuously has to send in money even though it;s small sum say like 20 or 40.00 but there is no way for this person to contact the company nor is there ever anything in the correspondence stating when the cash pay out will take place if it's true. Even the person playing the PCH sweepstakes is skeptical and said they are only playing for fun. Has anyone know of people to actually win the sweepstakes or should both people throw in the towel and quit while they're ahead because they're being scammed? Serious answers only pleas!!!!!