Recent discovery: some folks have had trouble using a credit card on my site if the card is issued by a foreign bank. Yikes, Authorize.net has some deep and obscure settings on that. I've now changed them to be much more accepting of foreign cards.
So if you're outside the States and have had your card declined on www.charliesplayhouse.com, try it again! I'll be keeping my eye on it from now on.
If it still doesn't work, please don't hesitate to contact me at firstname.lastname@example.org to figure out some other arrangements.
PS. I know PayPal would solve all these problems. Am working on that -- look for a website redesign in the coming weeks.