Erin,
you made your customers happy. Good on ya!!! I have never had anyone want a refund of shipping before on late packages, but if they ever did, they would get the full amount I charged them(including material costs). I would consider the lost $5-10 on shipping supplies that goes into one of my boxes as a cost of doing business and keeping my customers happy. But like I said, never had THAT problem before.
As far as the whole $100/shipped thing goes, that is kind of an oddball situation. It could go either way so easily. In most cases the shipping costs are calculated into the price initially, so no matter what, the customer IS paying the shipping, whether they realize it or not. I guess it just depends on how you view it. You could see it either as the seller has the shipping fees rolled into the price or that the seller is doing you a service by eating the shipping costs(even though we know this is pretty much never the case, but who knows?). Besides not shipping anymore for now, I would simply avoid the whole "$100/shipped" thing from now if I was me. I have used it before, but people ALWAYS got confused and still asked how much shipping was. It was TOO tempting to try and double charge them(of course shipping was calculated in my price to begin with). lol Also, should something go wrong and they want a shipping refund, that could get real ugly real fast with both sides arguing different ways, and neither one really being right or wrong.
Basically, my opinion is that, although it may be easy to type "$100/shipped" in place of "$70 plus $30 shipping," it isn't worth the possible risk of a customer dispute with shipping costs. If you spell it out at the beginning, they KNOW exactly what they are paying for on all sides.
And hey Erin, when you coming back through town? I've still got some tequila that needs drinkin'!!! lol