"The problem here is that it's almost impossible to review intent; maybe I really DID think my vacation was going to be cancelled, but then a project at work got cancelled so it came back."

Sure, people will lie about intent, not even be aware of their subconscious bias against black people, whatever...

That's why you look at the aggregate totals. It's just not going to be the case that coincidentally black travelers have their rentals rejected at a larger rate because of random external forces like renter projects being canceled.