A fool is his own lawyer, a fool is his own contractor, a fool is his own builder, a fool is his own realtor....
What do they do? They find you a home, one that meets your qualifications and specifications. They save you countless hours searching through newspapers, listings (which actually wouldn't even exist without realtors), driving out to see potential homes, negotiating with sellers, etc. Don't believe me? Hey, I don't care, go out and buy a home without one.
As for how to find out if a realtor is honest or not, that's easy. Ask them to do something (legal, please) that is in your best interest but not in theirs and see if they do it. For example, the easiest way to test this is to ask them to submit a low-ball bid on a house. If the realtor refuses, fire 'em. What they should do is warn you that the bid may be refused (and that such refusal could cost you the house) but do it anyway. Then you'll know.
BTW, what do YOU do that is so all-fired holy and important?