Paying duties and Tariffs

I am an American citizen who has been going to school in Canada for several years and am now returning to the States for grad school. Over my undergraduate I have of course acquired many personal affects (furniture, kitchen supplies, etc) that I am now taking back with me to the States. According to U.S. Customs and Border Protection I don't have to pay duties on these items so long as they are not intended for other persons or sale and have been used for at least a year.

Now both of those things are the case, but how in the world could I prove that for every last thing in my possession? On top of that some of these items were given to me by my S.O so I don't have any purchase history. Do border agents just kind of take your word for it? What has been your personal experience?