About the credit system:
When a person posts a CMT, usually a person finds what they are looking for, and they trade. However, sometimes, a person doesnt find anything they want, they may issue credits to them. Usually, this inspires trust between members, and a person pays off that credit in due time if they get new pokemon.
Usually, 1 credit is good for any pokemon in a persons thread. Or sometimes, people would charge 2 credits for a pokemon, which should be significantly valuable.
So yeah, i hope i was of some help! :3