I've had problems with Clickbank too. After a few days, I had sales of just over $120..
My account cheque limit was set to $50 (as I didn't expect to make money to be honest).
After a few weeks, I asked as to why I haven't had any payment for these transactions. I was then told that this was due to not having many transactions and that Clickbank needed to make sure the transactions were from different card holders.
In other words, Clickbank aren't prepared to give me the money I've earnt.. yet as they think that I may be using different cards to buy Clickbank products, in order to make commission.
Which to me is unfair.. as at $18 commission for the Product I've promoted.. It means I've at least 6 different sales.
Looks like i'll just have to get more, until I can collect MY cash.