how do they know what your ethnicity is.
I understand why places have those notes. Certain behaviors are more common with certain groups than others. It's not a genetic test. It's not about blood. It's more about likelihood of certain behaviors among some populations.
How do they go about it ? Show up and ask you ? Do you have to show proof? They do the inquisition before the act

Also i get Our black brothers for the most are well endowed so that can cause some problems, but what is the issue with Indians?
If you really are Indian and fool them into thinking you're Hispanic, they won't be mad. If you are Hispanic and you act like the kind of Indian they're trying to avoid, they won't like that.
If you really are black and fool them into thinking you're Metis, they won't be mad. If you're Metis and you act like the kind of Black they're trying to avoid, they won't like that.
If you lie on the phone and don't appear to be who you say you are when you show up in person though — that already creates an atmosphere of distrust that they were trying to avoid by excluding you.
The reasons sex workers have told me they try to avoid those groups are:
* not the penis size. Often these clients not even interested in sex. it's the pimp mentality. The girls don't want to be bullied or threatened into being part of some wannabe Iceberg Slim's stable.
* not really hygiene issues, though it does come up. The truth is these girls deal with that with all races. The main issue I've heard is a marketplace/bargaining mentality (like booking an hour and showing up with 3 others to argue that each should pay 1/4 of the hourly fee); shortchanging the payment or stealing it back when they think they won't get caught.
I've also heard complaints about clients so sexually inexperienced they expect a sex nanny (more work than just being an escort) or beset with some kind of madonna/whore complex, completely mistreating sex workers as lesser (and using that as rationale to steal from or shortchange them.)
I'm not a sex worker though, so take that all with a grain of salt. it's just what I've been told from the many I know.
I recount it because I think it's unfair to paint these preferences as a sort of racism from the girls or the agencies, when they're just practices, based on lived experience, designed to preserve their livelihoods.