con artist
1. A person who exploits the vulnerability of others for his or her own sake by manipulating and taking advantage of their confidence (the act of which is known as a confidence trick or game). It is the common abbreviation of the full term, "confidence artist." Be wary of con artists who send e-mails claiming to be a bank or some other trustworthy establishment: they often ask for your personal bank details to have access to your finances.
2. By extension, a person who is skilled at duplicity, cajolery, or self-serving manipulation or persuasion. John is such a con artist, always convincing others to pay for him on nights out under the pretense that he'll "pay them back later."