Hmmm,
I've had trouble with US customs and powder detergent. Never when mailed to the 'States, though.
Basically, the folks at the US border are under-payed, under-trained and treated like (explitive deleted) when anything goes wrong. They have to decide quickly about literally millions of items which they haven't a clue about (unlike here where the customs official can just call up the product data on the computer). It's understandable that they tend to be aggressive on these things.
I would, however, consider Canada or the UK. First, the UK has everything we have, just sometimes the names are different. Second, postage from the UK is often cheaper than from continental Europe.
Third, UK packaging is often more fun and playful than ours.