Election fraud was rampant in 2006 and 1988.  

It's almost certain that the PRI lost to the PRD, or I should say Cardenas, in 1988.  Miguel de la Madrid, the president '82-'88 admitted as much in his memoirs.

As for 2006, I know some people who were election judges who saw fraud before their own eyes.  I don't know whether it would have been enough to change the result, but it was still there.

And I'll give my consent to any government that does not deny a man a living wage-Billy Bragg