only people that rent "single bcx" commons/rares are potentially bot farmers.
the only occasion actual live human being rent single bcx common/rares is because its cheap and can get the job done fighting against other players/bot farms.

as far as i know, collection power or card level restriction on potential earning in each league does not stop people from farming the game with single bcx cards. joining a guild or using GF bonus is a common way of working around the system.

thanks michael for pointing out those basic questions in which i didnt really quite cover.

this is an idea i would like to turn into a proposal or suggestions,comments, and arguments is truly appreciated.