What do you say??

Like many women, I have a difficult time saying the word "no."  It isn't easy for most of us.  And this week I am encountering a lot of situations in which I need to be saying "no," but am having a tough time doing so.  
For example, what do you say when someone is sitting in front of you and says "Am I invited?"  Of course, you have no idea what to do and you just spit out "Of course." or "Why wouldn't you be?" or some other thing you aren't really sure that you mean in an overly enthusiastic tone.  I know some of my friends have passed the blame and you have even passed the blame on to me which I don't mind a bit.  Maybe you can teach me a thing or two and I will start passing blame on to you.
This afternoon, my biggest client called me to tell me that she would like to set me up with one of her coworkers.  Now I will be the first to tell you that I love a good set up.  I have met many a good man through my friends.  I always find it flattering that my friends think enough of me to set me up with their friends.  I also think that these people will have similar values and ideals as my friend whom of course has similar ones to me.  The key word here is friends.   I am not one to mix business with romance.  In fact I enjoy dating people completely outside my industry just because I don't need anyone telling me how to do my job.  I also don't want to know if he is not good at his job.  Let's hope he is, but you never know.  I also know the personality types of everyone in my industry.  This gentleman is what we call a "creative," the flakiest of all advertising professionals.  One minute they will be designing your billboards and the next they will be on a tropical island wearing a loin cloth beating a drum unfinished billboard left behind.  I repeat, they cannot be counted on.  So how do you say "Thanks, but no thanks."  In this case, I opted for "Currently, my dance card is very full, but I am always open to meeting new people platonic or otherwise."
I do feel there was a more firm response.  I will work on that.   In the meantime I will try to think of polite reasons not to meet this person.  Suggestions welcome....