Absolutely! Let them know.
I have purchased more from Healthshop.com than any other website. Never have had a single problem of ANY kind. Always outstanding products and flat-out GREAT service. This merchant seems dedicated to ensuring very happy customers and repeat business. I think they would WANT to know about your problem, to make possible corrections so it doesn't happen again.
As virtual says, be polite (sense of humour is always helpful, too...
), but for sure, let them know.