Guidestar is free, and it's great. I've had an account there since before the merger with Candid. They're a not for profit, too.

I would think that if the IRS cared to look at found rental activity reported, then they would be able to do rough math as to how significant that is. Whether it is 50/50 seems to be the question, and that also seems a significant enough question to pursue being informed. Doesn't the organization have their tax filings, say from 2018 and 2019?