If you are in a rush, i'd follow his advice and go to his manager.

If the project and relationship are long term I'd look for an opportunity to get his trust.

I've been in a similar situation before and over a few weeks/months I just kept persistently explaining my methods and demonstrating that I was looking to deliver the best results I could for his company.  In that context it worked for me to slow down and build trust.

But as a consutant you don't usually have the luxury of time, so you most likely have to escalate.

(PS  - a part of consulting is the poeple managment part.  You have to realise the story you are delivering, and how that helps the person you are working with.)

This situation happened a few years ago. I must admit I was slightly taken aback by the temerity of the individual; but I was equally sympathetic to the legitimacy of his complaint. However, after I had time to process his initial information, I realised that he wanted recognition. So I asked him if it would be ok if I include the source of the information (him) in my initial presentation slides. The assignment completed successfully and the Source got his due recognition and promotion.

My point: Its important to find out the clients/interviewees WIIFM (whats in it for me) is.

I've trained hundred-plus BAs recently and this dilemma always evokes some strong answers from delegates.

warm regards,

K