I know on our ebay if you ship through ebay, they just tally it up and bill you at the end of the month through paypal, so you don't even have to wait until your payment clears. I don't know if that's the case in the US, but it's no excuse to wait for payment if that's the case there too!
Unless there's a disclaimer regarding late/intermittent shipping, don't feel bad for dinging shipping stars - it's what they're there for!