The fight that might not even happen has already received big bets according to Westgate SuperBook and ESPN:
In mid-February, when hype about the fight intensified, the Westgate SuperBook made Mayweather a giant -2,500 favorite, with McGregor paying back +1,100.
Forty of the first 42 bets placed on the fight at the SuperBook were on McGregor, the largest a $1,500 wager at +800. Mayweather is now listed at -900, with McGregor +700.
The SuperBook has already taken more than $10,000 on the fight, which is by no means official. The book stipulates that the fight must be a boxing match and must take place by May 13, 2018, or all bets will be refunded. – David Purdum, ESPN