AirBnb could easily alleviate the situation with rejection updates. Although reviews leave far too much to personal opinion.
For now, at least, a demographic for each place would solve a lot.
"Oh 200 people have requested to be here and 100 were rejected. Out of that 80% of all black men who requested have been rejected and 30% white men and 0% of women, across the board... I think I'm good..."
This is important as hosts usually have 24 hours to respond. In that time period alternative listings I may be interested in could be booked. This has happened to me multiple times and puts unnecessary pressure/stress on me as a user of the service. If host can reject requests on a whim it lessens the user experience. I know IMMEDIATELY if a hotel has any vacancy, why do I have to hold my breath and pray an AVAILABLE booking goes through just because I'm black?
Except it is illegal to do so in a good number of countries. Racists know that. That's why they make up excuses.