Don't lie.

Seriously, I shouldn't even have to type a post about this.  Lying is both wrong and counter productive.  Especially in an organization where you are not the only employee.  What are you going to do tell everyone that you lied to a client and that they need to make sure not to contradict you?

Lying starts when you don't view the customer and yourself on the same team. the contentious nature of sales sometimes leads people into an us vs them mentality.  It is so much better to work with people towards a common and mutually satisfying goal than to fight with them to make and then keep a sale.

I am by no means one of these perky optimist types.  But I do think that there is a downward spiral associated with negative thoughts about clients.  When you dislike someone you justify giving them less and less acceptable treatment.  Soon enough it leads to the attitude that they are only one customer and there will be others if you don't treat this one in a way that retains them.

I cannot express how much better it is to work with clients who you like.  While it's not always possible, treat the ones you don't care for professionally.  Don't lie, don't cheat, don't steal.  And if you do, don't ask to work with me or my clients.