I use the duty finder because I want to run the content I have selected through it.
Sometimes this is just getting a clear, sometimes this means learning a new fight, sometimes this just means running whatever to get the tokens.

Do I expect people taking the Expert roulette to "gtg fast, clear in 10 mins"? Nope
Do I expect people taking the Trials roulette to know the fight Blindfolded? Nope

I do expect people that pick DF to have the correct gear equipped, to understand the basics and mechanics of their class.
And I expect people to be honest about their experience.
First time doing an instance? Say so, the bonus is giving it away anyways that you're new.
I simply don't expect anything from DF because as stated above, everyone and his pony joins it.

This also means:

1. Don't force your tank to run faster than he's comfortable with
2. Don't force your healer to DPS if he isn't comfortable with it
3. Don't punish DPS for performing badly

Instead ask people if they are open in doing so. Teach them what they are missing.
Too often I get negative cupcakes that ruin the experience for the whole group

You really can't wait those 10 additional minutes?
Then I'm sorry, but the DF is not for you.