Floyd Mayweather faced a very strong test from Marcos Maidana on May 3 of this year, but is listed as the clear and pretty heavy favorite once again for their September 13 rematch, as Bovada currently has the unbeaten "Money" Mayweather at -750, compared to Maidana's +475 underdog line.
Mayweather (46-0, 26 KO) beat Maidana (34-4, 31 KO) via majority decision in their first encounter, but may be swaying a lot of people by saying he purposely chose to make it a difficult fight that time, "for the fans," and that this time, he'll make it look easy and pick Maidana apart in a boring fight. (This is a tough PPV sell, but maybe enough people will buy just to see if he can.)
But while this -750 line does make Mayweather a pretty big favorite, recall that when the lines opened for the first fight, Floyd was listed at -1400 by some books, and -1000 was pretty much the agreed-upon stance just before the fight actually happened. He was without question a bigger favorite that time than he is going into this fight, though of course the money could move around, and this could wind up closer to -1000 for fight week once again.