Ideas for credit sinks.
Let players buy other classes ships for exorbitant amounts of credits. Every character I have wants to be flying the Agent ship please.
Have high credit cost options for more of the CC only unlocks. Like I get a CM mount, let me unlock that to account for credits. Same with appearance changes.
Have a credit option for converting bound to character items into bound to legacy.
Reduce the credit cap for player to player trades to 1bil or less, increase the GTN cap to unlimited. There will still be ways around, but it becomes far more inconvenient, time consuming, or risky so most people will not choose to use them.