There's one person here in Hauoli Mall's Battle Buffet that annoys me so much. A Black Belt / Karate guy with Hariyama... knowing Endure. In a buffet where one turn means one meal's worth and one extra battle and to OHKO them is a must. And most of time, he would be in front of a golden dish. Why!!
Those Office Guys with their Sturdy Magnezone, I can still tolerate with Lunala, but not this guy that ensures you will waste a turn unless he doesn't use it.
Ugh, to get the most money from the Battle Buffet I figured out who to battle and who not to battle quickly:
1. Both Office Workers are a no go, unless you have a Pokemon with Mold Breaker or uses a multi-hit move. The money they give out isn't that great anyway.
2. If you can, don't bother with the Preschooler and Youngster; only battle them if you're other options are the Office Workers and you don't have a way around Sturdy.
3. The ones you really want are the Gentlemen and Madame (the elderly trainers). They pay out the most but watch out for the Madame as her Seel is bulky.
4. Other notable trainers are both Sightseers, the Rising Star, and Ace Trainer. They give out a nice amount of money.
5. Meh ones are Beauty, Cook, Lass, Breeder, and Black Belt.
Now if you're just going for top score (which honestly doesn't matter until you're versing the Buffet Queen post game) your goal is to KO them on your first turn while going for the bet platters as possible (many of them have stalling strategies if you don't do this). Forget about the platters occupied by the Office Workers, as annoying as that can be, just focus on the ones for the trainers you can OHKO. Learn what Pokemon they use and use type advantage or overpower them. Remember you can save between battles.
Now if you're going for money that's a whole different strategy. You're going to have to be quick as you'd want to activate Roto Prize Money to triple winnings. Than you'd always want to make sure the Pokemon your sending out has the Lucky Coin equipped. From there you're good to go except for two things if you also have a Pokemon that knows Happy Hour:
1. If a Gentleman or Madame appears you hit the jackpot! Send out your Happy Hour Pokemon and have them use Happy Hour on the first turn. Then either try to knock them out on the second or, if you don't think it's possible, switch to a Pokemon who can on the third. With Roto Prize Money + Lucky Coin + Happy Hour they pay out BIG.
2. For your last opponent you don't got to worry about turns so, no matter who you're facing, just Happy Hour on the first turn to try and squeeze as much money from them as you can.
NOTE: If you can, see if you can try saving a Gentleman or Madame for your last opponent.