This all boils down to a single statement - "Trust, but verify."

If you have the ability to trust, then make sure what you're getting involved with is truly what they say it is.

Pressure to make immediate judgements are suspect. So is any statements like "I'll never steal from you" or "Trust me... because...".

Most people don't have to qualify themselves immediately using those statements. That should be a red flag right there.

In any case, anything that promises a large return in a short period of time should be viewed with a healthy dose of skepticism.