Are We Going To Do That?! - My Secret Hobby, #5

When Mark first gave Crystal her test drive and introduced her to the Hobby she was a novice at the whole pay-to-play Community.  Now after only a few weeks she's one of the most popular escorts around.  Despite her popularity and promiscuity she's still Mark's ATF and tonight he's booked her again, but she doesn't realize that there's something he hasn't done to her yet that they're going to do tonight.
Even though Mark is twice Crystal's age he's the only man she's every felt totally comfortable with in bed, so when he asks her to push her inhibitions to the final level she's OK with anything that he wants to do with her - and to her!  Afterward she can't believe she's waited this long to explore the final frontier. Emboldened by her new-found experience and feeling a little feisty, when Mark's neighbor Sarah comes to the door (the same Sarah that was completely, publicly uninhibited in Something Special) Crystal decides to play with Mark by seducing Sarah, only to discover that she knows more about her than she realizes.
Here's an (edited) excerpt from the book:Sometimes when I see him, before we go BCD (sorry, 'behind closed doors') he has me do a slow striptease for him.  Other times he will slowly undress me, fondling me.  Once he started in the living room, and thankfully he'd already taken my top off because he caught me off guard, if you know what I mean?  And once, he must have been especially anxious for me that night, because right after the front door closed he took me to the sofa, and when he was finished it was only then that he offered me something to drink.
The point is, every time I see him it's just a little different, but I am there for him, to do with me as he pleases.  Tonight he says we are going to do something we haven't done before, and I am anxious to discover just what that might be. He toys with me ever so gently.  "Why don't you go into he bedroom and get comfortable?" he says.  "Sounds good to me, " I smile and walk into his by-now-oh-so-familiar bedroom to take off my clothes.
When Mark comes into the bedroom I am on display at the foot of the bed, offering myself to him."Very nice, Crystal, " he says, stroking my hair and I can feel his appreciation as his eyes pass over every inch of me.  He is still fully clothed and I watch him from my pose as he moves around the bedroom lighting the candles.  He pauses as he passes me to take me in his hand, enjoying my warmth.  He walks behind me and pats my behind, allowing his hand to linger on me, then spanks me, not too hard, just hard enough to leave a lovely pinkish mark.
 Involuntarily I let out a grunt and bit my lower lip.  "Too hard?" he inquires."No.  Actually I kind of like it."  I feel my self starting to get excited."Oh you do, do you?"  He pats my other side as if taking aim, rests his hand and lifts it .