Although Momo's ditzy response to it helps null a little bit of the fuel, it's implied Balio and Sunder may molest her or worse when left as the hostage at the Contest of Champions. Considering their track record, this is nothing to consider too far for them, but thankfully nothing ever results of this.
Balio and Sunder themselves are outright ruthless. Some kids are stealing money that interferes with the mafia's profits? Burn their house down and personally try to kill them all. When they encounter Ryu on the mountains shortly thereafter, they quell their fears of thinking he's a ghost by stabbing him in the back outright (until he recovers and turns into a dragon at least). And then they stick him in a cage to try and make money off of him, only for his transformation to revert and thus have the King of Wyndia arrest them all for deceit. Then they exploit the princess Nina's naivete, knock her out, and would've tried to ransom her if it weren't for Ryu yet again. These two have absolutely no morals, and while at first they may seem like a Goldfish Poop Gang, they'll exploit or kill anyone for a profit.
The terror that is Rei's Weretiger form. He intentionally keeps it under wraps so he doesn't harm anyone due to a lack of control, and after the Time Skip, he all but brutally murderizes the hell out of Loki, the guy who's plan got Rei's friendship with Teepo and Ryu torn apart by the mafia years previously.