This happened to me and NearFantastica on some frags he sent me. In that case, though, either U.S. Customs or Canadian Customs (we don't know which) just sent the parcel back to him. (He then re-sent it to me, and it WORKED that time!) I know this sounds awful, but all I can do is recommend that you re-package the whole megillah, label the form "used cosmetics with a value under $20.00 CDN" and re-send it. Customs agents usually just do spot checks and random checks, I think.
If THAT doesn't work, then a refund's in order, of course. Make sure to keep your buyer abreast of the situation as things unfold.