What is the difference between a pro and a con?

I believe Zig Ziglar once wrote, "... the difference between a pro and a con is INTENT. The techniques used are the same... but what you plan on doing, on achieving are different."

Normally, the Words pro and con are used for opposing positions, for and against. However a pro would be a professional, and a con would be a confidence artist (i.e., a person who commits fraud by deceiving others after getting their confidence). In that context the difference between a pro and a con is that the pro delivers the goods, and the con is fraudulent.