Aside from almost everything said above I'd like to add that LFM's are like posting a Job opening:
1)First and foremost the whole idea is for you to get the people you'd like to play with join you in your quest, so be clear and honest (If you are going to be a jerk, so be it; be a jerk from the get go, less chance for an argument later)
2)If you want specific classes make sure they're indicated in the posting and keep it updated, same as difficulty both in the difficulty selection part of the LFM and the comments (for those "technology challenged" players who can't hover over the mose over)
3)If you have saved spots say so and make sure it is reflected on the classes you require.
But it is not all you, on the other hand you are asking for help so as such you must respond accordingly. Unless you post "Will MyDDO" or "Selective" or something of the sort, if you ask for a certain class and level and the appropriate class and level apply u have 2 choices, accept him or send a tell explaining why you aren't going to. Sound like work? It is but think of it the other way round: You apply for a job and you meet all the requirements and not a peep from the company... kinda mean no?
And if you've ever been in charge of recruiting you ought to know that even if you screen people sometimes they have a way of surprising you so aside from making you requests crystal clear most of the time you'll end up with high expectations and nothing else. Relax in the end you'll find people like-minded and those people then to gravitate to one another.