I'll let Dean handle this for the heavy stuff....
...but if you own 600 points and only want 200 for yourself each year and intentionally bought more than you will need for the purpose of renting, then I would say you are a commercial renter.
It goes back to exactly what Disney has said..."pattern of activity." While this is ambiguous terminology, the principle is valid. If you have a year or two where you cannot use all 600 of your points, sure, go ahead and rent them. I have never heard anyone here have a problem with that.
However, if you
purposely over-bought so that you could rent...and thus year after year after year (pattern of activity) are renting out numerous trips, then I would classify that as a commercial renter.
FYI--Disney's current test is 20 reservations in one year to people other than you. Thus, 600 points would not be on their radar as you really can't book more than 20 reservations with that number of points. (Ok, yes, you can book more than 20 one or two night studio reservations, but you get my point.)