Uncanny, I have just commenced a consultancy in an organisation where one of the big 3 outsourcers messed up a project to the point where there is an unworkable situation in the workstation environment. There was a signficant role for the client as they do believe one can segment IT areas to the point where due dilligence and testing are dirty words.

I try to keep my constructive criticism close to self - in my experience bla bla bla, here is what I've done for other clients, typically bla bla bla.

Unfortunately, there are remnants of the old project team who express an amount of aggression at a mere whiff of any criticism so I need to be really careful. In a roundabout way you are exposing a level of incompetence and that means sometimes you get shot as the messenger.

Never bad mouth, stay side by side with the client, and sometimes with the previous consultant as there are situations where the previous person is still there.

This is probably more norm than exception, and can cause a lot of stress and angst, both in the client and for you, as the consultant.