Very good thread - but I might have to kinda disagree (but maybe not) with "should never start a hand specifically looking to bluff it." I say "kinda" only because of the word "specifcally". If you mean by that you should not start a hand thinking you are going to run a bluff by hell or highwater (do it no matter what) then yes - 100% agree. And I do believe that is what you are saying
However I think it should be said that it is okay to look for those opportunities when you see a table or an opponent who is susceptible to it. I just did this last night a couple times at my table (tight passive) and pulled them off. Where the OP went wrong (and many other people do) is not realizing that pulling a bluff off is like waiting for the perfect storm. A lot of factors should align before that "spot" to bluff is open.
If you are not playing on a level that defines "what does my opponent think I have (or does he even care?)", then you probably should not be trying to run too many bluffs (or even looking for those opportunities).
You have listed one factor - what level is your opponent playing on. Does he even give a thought to what you might be holding? If not, he is just not very bluffable. If he has top pair he might go to his grave with it (especially if he has a kicker to go with it).
Some of the factors that need to align are (in no particular order):
Table Image - Yours and Theirs (CRITICAL POINT - Is the other guy even thinking about what you might have? If not, bluffing is pretty pointless)
Board Texture
How Many in the Hand
Stack Sizes
Table Limit
I'm sure someone else can come up with some more (or elaborate on what's there) - I'm just not a patient poster
But IMO I think it's okay to look for those opportunities when the factors needed present themselves to you. You just need to know the factors and determine if the perfect storm is presenting itself to you.