Years ago I was hosting guests from Airbnb. Due to my location I got a lot of English language students coming to Canada for 2-3 long immersion courses. One guest shared with me that one of their assignments was to engage with hosts, even if they weren't planning to ever book; obviously these people eventually did, but it's a bit problematic as it's time not compensated for - sure, it's built into the cost of business but without an agreement to accept such practice conversations it's verging on dishonest.
You'll never see a penny mind you, but IME (which includes getting pimped out to help the admin office a decent bit in grad school) mystery invoices have a pretty good chance of getting "wtf is this"'d all the way up to the dean's office.
