Heya, welcome to the forums.
... <snip>... I've been selling a lot of cards I don't use for money...
"Rule of Thumb Number One: Never sell upgraded cards unless you have more than six copies, and never sell unupgraded cards unless you have over 12 copies total (unupped and upped)."The above italic quote can be found within this thread's opening post:
Money Management (by kev)If interested, you might find it is a good read.
Enjoy your stay here.