I believe you may have to contact them for further information with respect to how the rental income is calculated and reported to you.
However, I do find it somewhat disturbing that the deduction is referred to as an "itemized deduction", which usually implies that the deduction would be taken on Schedule A; it's not. Any deduction would be reported on Schedule E or Schedule C, not Schedule A.
Regardless, if you report the gross rental income on your return, then you should be able to deduct any fees that AirBnB deducts from that gross amount.
FWIW, I have firsthand experience with VRBO and can tell you that they do not deduct the fee charged to the guests (renters) from the amount the owners receive; only a small commission is charged to owners which, in turn, is deductible.
