I think the problem is vendor managers who were never searchers themselves, and don't have lots of experience yet.  The end user rarely cares about what goes into an order, and a green vendor manager won't be very good at explaining delays to their customer because they do not understand themselves.

 I try to always set up expectations with new clients that there can never be a set fee or turn time for every search, because some searches could take days, or even weeks, to complete - and we need to charge for our time.  Then, if someone else from that company starts questioning us, we can both explain that it is the nature of the work - anyone competent is going to take just as long and charge as much.  And I can point out that we agreed at the beginning that we cannot be held to missed turn times, so long as we have good communications.

 Vendor managers are going to push - but when I know I have the best abstractors on the job, I don't sweat it too much.