My perspective hinges on the combination of two things: your imagination and your interview of him. If you are a professional (versus lifestyle), I think you have to communicate with your client who has to reciprocate (it is a business relationship and he won't come back if you don't give him what he feels he is missing).
Some guys want the limits pushed (i like the concept of predicament bondage)similar to what EW said. Some guys want mild pain, some want a lot, most have different ideas what is actually painful; line of clothes pins around the balls may be too much for one guy, just perfect for another, and child's play for another. When I go to the hardware store, I look at things and think about how each item could be used on me.
I hope my ramblings have shed some light for BB.