A con man is someone who scams money out of someone by gaining their trust. The nice lady emailing an offer to share her two million dollar inheritance with you is almost certainly a con man.
Con man is short for confidence man, a name that comes from the part of their scam in which they gain the confidence and trust of a victim. If you're taken in by a con man, you have confidence that they're honest — you're convinced they will invest your money or deposit thousands of dollars in your bank account. Other names for a con man are con artist, grifter, or scammer.