Take advantage of it- the deal is worth it. Around the pool in the main room is where you'll find the Water Club members. First up to the table is Amanda, and she can be tough. Expect to see strange cards like Wigglytuff Lv36, and be prepared for Amanda to use Trainer cards to heal her Pokemon often. Play cautiously, and you should have little problem.
Speed is essential here, but so is caution.
The final member blocking your way to the Master is Joshua. You have to keep up with him. Luckily, he seems to have a low energy ratio in his deck, and sometimes finds himself unable to power the cards he plays. Take advantage of this with an energy removal strategy, and he should cause little trouble. Of course, after Joshua comes Amy, the Club's Master.