Sometimes there is a bit of lag in the system
Buy a low end card and it will clear
Once i had sold loads of cards and didn't get the amount of clintz i was supposed to.
I looked in my purchases history and had somehow bought a Esmeralda for higher than market price
No idea how it got there, owner didnt want it, sold it
Known issue. Your money is there, its just updating your UI that lags for some time.
You can spend that money even if it does not show on your screen, as long as the trade has happened.
You can check your real balance by opening home page and then navigate to "Friends News" tab. There are messages about trades done, and the amount in "In the bank" part part of the message is most reliable information (tho not 100% accurate, it can be offset by few trades if you do lots of trades on busy day.)
Anyway, it will always end up being correct. Your real clintz balance is stored in market subsystem, its just hard to get that information out of there constantly. Maximum lag I have seen is about one hour.