A Pokémon Connoisseur is a person that tests the connection between trainer and Pokémon. There are four ranks; S, A, B, and C, with C being the lowest while S is the highest rank. In the anime, Cilan and Burgundy are known to be Pokémon Connoisseurs. Cilan is a rank A Connoisseur, while Burgundy is a rank C Connoisseur. Connoisseurs refer to their top Pokémon as their "premium brand" (japanese: ビンテージVintage). Pansage is Cilan's premium brand and Sawsbuck is Burgundy's. It is shown in BW025 that Connoisseurs also use the premium brand term for other Trainer's Pokémon, as Cilan mentioned that Pikachu is Ash's premium brand and Axew is Iris's.
Only classes A ans S are allowed to test the compatibility between Trainers and their Pokemon. Classes C and B are only allowed to assist these classes.
According to Cilan, the compatibility can't be determined "by the book", and all connections should be judged from each Pokemon's unique qualities.