i would have preferred it if the artist had done the last panel like this instead:

Kyouko: Oi Sayaka, you're getting really good at conning people.

Sayaka: I learnt that from you.

Mermaid Tears sounds like some kind of ingredient/fusion part/gem/combinable junk/monster drop.

Parody of "Sale of Toad's oil"

http://www.youtube.com/watch?v=LSm_3TIlLRk