That she doesnt see every gent that calls and emails her. That she likes to have chemisty with her partners.

that she will have a stingent screening process that most likely includes requiring several references.

At least that's how I'd take it.

It could just be marketing speak as well.

It can mean anything from rigorous screening to low volume to a simple marketing pitch. What it DOESN'T mean is that you are guaranteed any sort of better experience simply because a lady calls herself "selective".