The FAA is quite clear on what is commercial use:

" The FAA has consistently defined commercial operation in terms of whether the operator receives direct or indirect payment for the operation. It is not necessary that the operation be conducted for profit or even that there be any intent or ability to make a profit. The compensation is not just limited to monetary payments but includes anything of value. This broad definition of compensation has been affirmed and adopted by both the NTSB and the federal courts. Administrator v. Roundtree, 2 NTSB 1712 (1975); Administrator v. Mims, NTSB Order No. EA-3284, review denied 988 F.2d 1380; Consolidated Flower Shipments, Inc., Bay Area, 16 C.A.B. 804 (1953), aff'd. 213 F.2d 814 (2nd Cir. 1954)."

This is from a law firm!