Perhaps I can add that the exemption was drafted to recognize that this is something where some judgment will have to be exercised, first of all at the border, and second of all if it ever gets through there, later on in a courtroom.
To put it one way, a commercial quantity for, say, marbles would be maybe a thousand of them or more. For ocean liners, it would be one. You really cannot set out particular criteria saying which circumstance is a personal use circumstance versus which circumstance is a commercial circumstance.
There are so many different goods, and so many different sets of circumstances, that this is something that will have to be determined at the border, using the judgment of customs officers. If they are of the view that this is a commercial situation and the person disagrees, they can then follow through with a courtroom and see what the court decides.