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


If I buy a component from someone in Canada and want them to ship it to me in the US, what should I have the seller do to get it through customs?  I'll probably tell them to use the Canadian Mail to USPS.  
Are there forms to be filled out & maybe attached to the outside of the box?  A copy of the receipt attached to the box?   Something else.  My total purchase amount would probably be $1,000 or less.
How expensive are the US customs rates?
Thanks,

toolbox149

Showing 2 responses by toolbox149

Thank for the help.  
Is there a form that needs to be filled out to get a parcel through customs, and if so, can I get a copy from somewhere so I can send it to a seller prior to the seller getting to the post office?

Thank you to all!   This is a big help.   I intend on requesting that anything I buy be shipped Canadian Post or FedX.
Thanks again.