The ultimate con for me was the con perpetrated by the WWF that they were the "only game/best game/only thing that mattered in wrestling" starting in 1984.
Consider first that this con was aimed IMO at non-wrestling fans. It did work beautifully on casual viewers in this regard. Think about something as simple as a News station giving credit to all pro sports brawls in hockey, baseball, et al as "looking like something out of the WWF!". Now think of every sports station in the country making a claim along those lines, which did develop over time, for years on end, continuing to this very day.
That's just one example, but the brainwashing was brilliant as it begun in the news media and used them as a tool to implant the idea of "WWF" into the mentality of people everywhere, regardless of their love or hate of Pro Wrestling.
After 1984, everyone I ever talked to that despised pro wrestling always referred to the WWF while dissing wrestling.
Vince said "we're the best" over and over and over until everyone believed it, true or not. Promoting at it's best, some would say. but the target audience was not the wrestling fan as it existed pre-1984, it was the non-fan, and the development of the WWF as the representative symbols for pro wrestling as a whole in ALL situations, good or bad.
THAT is in my mind the greatest con ever perpetrated in pro wrestling history.