You get a call or postcard from someone telling you you've won a prize and asking for payment to buy something, for processing or administrative fees, for customs, for taxes, or any other reason. Legitimate sweepstakes or prize offers don't ask for payment because it's illegal. The person says you have to take the offer immediately or you'll miss the opportunity. Legitimate companies don't pressure people to act without time to look into the deal. The caller refuses to send you written information before you commit to anything.
Legitimate companies are always glad to send information about what they're offering.
The caller claims that you can make huge profits in an investment with no risk. All investments are risky and legitimate companies must and will tell consumers about the possible risks involved. The caller claims that you can make huge profits through a franchise or other business opportunity with little or no effort. All business ventures require knowledge and effort on the part of buyers, and no legitimate companies would or could guaranty profits. The caller is asking for a donation but won't tell you exactly how the money will be used and how you can verify the charity and what it does.