Re: charities
Some (maybe all?) charities declare running costs and with a bit of research on the Internet, it is often possible to find them.
We decided to give a regular monthly amount to WaterAid but not before looking into how the money is spent. The organisation declares that for every £1 raised in 2017 to 2018, 72p went on delivering services and making change happen, 27p went on fundraising and 1p on governance. I'm assuming that governance means wages and administration.
There has to be faith that the annual reports charities give are correct but I'd think they are all auditable.
https://www.wateraid.org/uk/our-annual-reports