Agree with Catherine that being emotionless is not an asset - it always helps if you can chat to a client in a warm and friendly manner. But "super friendly" isn't necessarily a positive factor: it can verge on the creepy or intrusive.
It's a two-way street as well: I tend to react in how I think is the most appropriate manner for each client - some want to talk, some don't; some are very curious about me, some aren't; some know exactly what they want to do and so long as I'm happy about it I'll let them get on with it, others want direction or some ideas.
I can nearly always find something likeable about a client, whether it be looks, personality, or what he does and how he does it. As such, nearly all my meets provide me with some physical pleasure. And with the odd client where that's not the case, I'm just polite, professional and get on with it. It's not acting - it's being a nice, decent person!