pg ramble warning 
I think there are three sorts of concerns over auditions that have't come through an agent/normal channels or are not with an established casting director.
(As you have an agent, I would be inclined to check it out to see what his/her opinion is by the way, both in terms of legitimacy and whether it is worth your while).
The first is: Is the person running it genuine? i.e. are they actually planning to make a film or are they running some kind of a scam (and that could be a financial scam or the sort of scam where they trick people into behaving in a way that they might come to regret at a casting). If you suspect this sort of scam then common sense will save you from losing money or losing anything else! I'm sure you are sensible/experienced enough to walk away from anything that turns out to be like this ruby95, and if you are worried in
any way then taking someone with you is definitely the sensible thing to do.
The second is: is this something where the subject matter/style/script is something you are not sure you want to be involved in. As you have already seen the script, this isn't the case here, but again this is reasonably simple to tackle - if you find you are not comfortable with anything you just walk away.
The third sort of concern is sometimes more difficult to make a decision about:
Can you afford the time/money to go to an audition for something that might turn out to be a waste of your time in terms of the quality of the product? If you are being paid, I think this is less of a worry because even if the product isn't brilliant, you have money in your pocket and a credit on your CV. Mind you, if it has not come through an agent, you need to be careful you are not being fleeced ( I always check things out with my agent, she has sometimes managed to get me a better deal - even counting her commission) . If you are
not being paid, then this is where the judgement call comes in - and sometimes you'll get it right and sometimes you'll get it wrong! Not every unpaid job is worth doing. It is very common (and understandable) that the person producing the work will be enthusiastic and optimistic. It is also very common for producers/directors to massively exaggerate the likely importance/credibility of their work - and this is where it's up to you to be the realist and understand that all the grand plans can come to nothing much in the end. If you go into it with your eyes open to this possibility and you are prepared to say no at the audition stage if it doesn't feel right, then if you can afford to go (taking someone with you if you want to) I would recommend doing so.
Told you it was a ramble...
