the ways iirc arent different, it's usually just the strongest/most relevant trainer in town, either according to the league or by referral
anyways, question: is/was crescent aligned with indriad? if we assume that indriad was the one with the yveltal who set keta's house on fire (wll), and crescent the one who set on fire wispy tower, wouldn't it make sense? although there is one weird detail which should be pointed out: indriad was apparently able to spy on team xen (an organisation which for most of its existence has been underground) but couldn't use it to figure out who vivian