I don't think there is anyway you can say that you don't see xxx without seeming rude / racist to those guys.
Probably totallly irrelevant & nosey but is it just black guys you don't want to see because you might know them or do you not want to see other ethnic minorities
Generally speaking if I speak to somone on the phone I can generally tell if they are a black guy or not
Don't know how but I just can, but then again I saw a black guy who spoke like Prince Charles recently so not always the case
My friend who is black wont see black guys for the similar reasons you wrote but will see other ethnic guys
I find backpage works well in areas where there is a high ethnic cliental base pretty much the same for viva St
In place like heathrow 70 percent of my Clients I would say are black / asian and a lot of them mention that girls won't see them and its Similar in Reading & Birmingham
It's worked well for me in Birmingham & Leeds as well
( same for viva St)
While it's cheao and cost effective I don't mind paying a few pounds a month to advertise if get one booking a week from it then it's worth it