I was one of the gullible and had to learn the hard way that stats mean very little. Clinics definitely can cherry pick even with DE cases. Old eggs aren't the only problem that clinics have to deal with so just because you are doing DE doesn't mean they can't eye you warily if you have some other issue that means you won't be an easy success for them.
It's disgusting, really.
I much prefer to give my money to the clinics who try to help everyone, but unless and until the word gets out that stats are not the whole story, those ethical clinics will be at a disadvantage while the sheisters get all the customers.