I work as a machine learning consultant. Because of the nature of the beast, we (my team) spends a lot of time in researching papers, submitting to conferences, making patent submission etc. (2 patents pending) As such there is a lot of IP & domain expertise involved.
A new client (ex Bain & from one of the top schools) sent a one-sided NDA before he could share any more details regarding the project.
I thought it was fair if I asked for a Mutual NDA. But then he came back saying that he was the "client" and I the "vendor", so it didn't make sense for him to sign it. I tried to explain that there was a lot of IP involved in any engagement, and a Mutual NDA was just a hygiene issue, but he was adamant about it. So, I said it's okay --- it doesn't make sense to go forward with the engagement.