If you are working with a business that feels the information it needs to share with you is a trade secret, it is both arrogant and unprofessional for you to second guess that customer. Especially if they are a startup, that trade secret may be literally the only value that company has. I would never work with a supplier who refused to sign my NDA.

The third one is a more legitimate concern, but you have two options:

1. If the idea is already public, just point them to it as soon as they tell you what it is. “Hmm…an online classified site. That’s an interesting idea; have you heard of Craigslist?”

2. If the idea is not public and you’re under NDA for it from another client, just tell them immediately that you have a conflict and can’t take the conversation any further. This is the right thing to do anyway, regardless of NDA status.

I’m not advocating that you sign everything blindly, but NDAs are almost completely worthless most of the time anyway, as any competent attorney could find plenty of examples of public ideas (see your point #1).

Most NDA’s in ANY business are rediculous now and a huge potential litigation bomb later.

Basically an NDA is something that puts you on their short list for future possible litigation.

I had run in with people who wanted me to sign NDA’s before designing their website and I countered them this way.
“Don’t tell me your unique idea. Just tell me what the website needs to do.”
I don’t need to know you want to make a social network for people who refuse to sign NDA’s. I just need to know that you want the user to be able to communicate with others in a certain way. I don’t care who they are or what group they are in. I am NOT going to be advising you on that group or how to market “your” business idea or how to improve it so I don’t need to know the niche AT ALL.

I other businesses I don’t sign NDA’s either. NOt for job interviews either ( although sometimes I give THEM a piece of paper that says if they use any info I GIVE THEM during an interview they must compensate me.

One of the keys to having an enjoyable life is avoiding lawsuits.

One way to avoid lawsuits is not EVER sign something that says you will owe someone else money or damages if you disclose what THEY should be keeping secret.

Keep the secret part of your idea secret. I don’t want to know it. Just tell me the non secret stuff.

If I have to know the secret stuff to work on your idea then I am in fact INVENTING what you claim is YOUR secret idea and I won’t do THAT for standard pay.

Incidentally often if you do sign an NDA the first thing you will learn is the idea is something you have already heard of and the second thing is they will want you to improve their secret idea.

Given the client’s good intentions, why don’t we sign NDAs? We have a few good reasons……