Honestly, I'm not really sold on this whole "do a 1v1" thing for a couple of reasons.
First, it's that Fang probably has a better chance than Maelstrom at beating the Gligar, given that Fang is a full rank higher than Maelstrom and has an Ice type move.
Second, there's the possibility that the other grunt will just throw out another Pokemon after the 1v1, one that we might have need Maelstrom or Fang to beat, had they not been tired in a battle.
Third, this guy is a criminal. I do not want to give them some of our hard earned money if we lose.
Fourth, we probably have better odds in a double battle. We'd be able to focus in on type weaknesses of the opponents easier, and I highly doubt that two grunt-level criminals will be able to counter or pull the type of combos a Pokemon protagonist can.
Fifth, doing a 1v1 battle doesn't really feel appropriate, right now. Like, they're criminals wanting to silence a potential witness, hell yeah they're gonna bumrush us with two Pokemon at once! Like, why should these grunts, who are worried about being seen and arrested, give a damn about what kind of battle we want to have? I dunno, it just seems kind of weak to turn our first encounter with criminals, which by all rights should be a desperate thing as they fight to silence a witness, into "LETS HAVE A POKEMON BATTLE GAIZ!!!!"
Anyway, that's just my take on it.