The groups as far as i know or at least the ones i have heard of do hold their end of the bargain. They can get themselves in trouble by scamming Gil and it's not really good for business to get a rep as a scammer i am sure.

You could just do like the majority of players who have relics and join an FC with people willing to carry you through it. That way you don't have to pay a chunk of gil. The going rates seem to be 500-700k for a win buy. Unless you have huge amounts of gil then it's the fast track XD. Though if the problem with Titan is yourself and not the people you group with then i'd recommend finding people who can help you learn the fight and not just pay so you can die and skip learning anything from it.