If a promise sounds too good to be true, chances are it is. That particularly goes for offers that require you to act immediately, or success rates that are too good.
"If someone offers you a guaranteed high rate of return, they're lying," said Donley. "You're probably looking at a fraud."
Sales pitches that lead you to believe that the offer is only available for a limited time or restricted to a special group of people should also be a red flag.
And watch for any information that comes with free offers, such as educational seminars that provide lunch or mail offers that include trinkets. Those will make you more likely to respond.
"You have a tendency to believe this person and trust this person," Walsh said. "The one thing we always say about free meals is you don't have to bite on what's being offered."