3/ Creation of a top 100 of sellers, the top ten of every month get a free NB pack
of the cards supposed to come a week or 2 later (maybe those cards can be sold, maybe they can't, like a ld)
4/ special place in the market where you can sell your Cr's to a discount. The bigger the discount, the more bonuses, special missions etc, you get.. works with credit vs cr's thing too.
5/ Stop choosing the best, key cards of their clan to turn Cr and go back to the old way of turning a commun card cr.. It's not nearly as fun to have a huge amount of lousy unplayble cards compared to having a dozens of marco's
Understand that players try to keep on to their Cr's because they won't lose value with time like some rare expensive cards and they will probably go up (way up).
So the idea is to try and stop some Cr's to go up( and maybe down too) in price in a ridiculous manner.
1/ Some other games do that, you control the maximum price certains cards can be sold for. You know how many Dj's are out there, so you can evaluate a max prize.
2/ When a player have more than a certain number of one specific Cr, every month they all lose a % of their value (except for the first one maybe). You get the average price of Dj for the past month, if a player waits a year to sell his 14th Dj, he can't sell it for more than 2/3 of the average value. Only works with expensive Cr's.
3/ Have more ideas, because I'm out !
Hope it helps !