This is not like ordering a la carte at a restaurant.
If an escort has an ad or website that mentions services, go with that. Otherwise try to use reviews. YMMV. If several of her reviews mention cbj and only a few bbbj, count on just getting a cbj.
You will know even less at AMPs. Imagine calling the AMP and ask if they provide FS or BJs! You know the answer will be “no” even if it’s available. In fact, several years ago I looked at the reviews of an AMP (since closed) and every reviewer stated that only HJ was available. Yet, every time I went there I got FS. Sometimes you get lucky.