They're a different kind of trainer--based on their abundance of knowledge and experience, a Pokemon Connoisseur tastes one's skills and determines the capability between a trainer and their Pokemon. We can advise new Trainers on selecting their first Pokemon, or on their raising methods and even move choices for those who take an active part in battles...

[...Though, it's possible we may have to simplify this a little more, as it occurs to him that he's explaining all this to a kid.] ...In short, our job is to help a trainer and Pokemon on improving their relationships with one another so that they may become better friends.

[Think something like a marriage counselor...but for a person and their Pokemon rather than a husband and wife?]