What do I need for customs if purchased in Canada & ship to US?

Xpresspost USA and Expedited Parcel USA:

Name, address and phone number of sender
Name, address and phone number of recipient
Non-Delivery Instructions - (Return at Sender's Expense or Abandon)
Reason for Export (Gift, Sale,Document,Repair/Warranty,Commercial Sample, or Other)
Quantity,Detailed Description of Contents, Net weight, Declared Value in Canadian Dollars

I never bother with the net weight.  They do that anyway when I take it to the post office.  I also usually fill out the country of origin and HS Tariff No. from the Commercial Senders section to help avoid confusion.

I have no clue if any of my buyers have been dinged with duty, taxes, etc.  I just warn that it is a possibility.  I never send UPS or Fedex, as I am working under the assumption that they are doing the same sort of charges on CDA>US that they do on US>CDA

I recall when I bought a pair of Coincident speakers from Canada, UPS called and needed my SS#.  At first I thought it was a scam call, but I was told when anything over a certain value was shipped to the US the Patriot Act, or something like that, required the recipient's SS#.  Turned out it was true.  I don't know if it's still true.  

This is why i buy in USA only.Good luck.