For those not accustomed to ordering online, "invisible money" means that you time your order so that both the original order and the credit for the return (if you have to return it) hit your credit card in the same billing cycle.

I hope, of course, that you're paying that credit card balance in full each month to avoid the exorbitant interest charges! If you're not, "invisible" definitely does not apply because you'll be paying 20-25% interest in the meantime. Pay off your credit card balance before investing in gear or anything else--you and your wallet will be far happier in the long run!