And the minute you recognize it, you stop and discuss your new findings with the customer.

I've gotten the response that I agreed to this or that and I should take care of the network problem "on the side". Generally, I can explain the difference between networking a printer and fixing the network and why the two are different and why the costs will change.

There are times that you find yourself doing a bit extra. I never mind that. I just make sure that the customer KNOWS that I am doing a bit extra. Value add, and all that!