FSP has a nice post up today about answering difficult post-talk questions.
I haven't had too many post-talk questions that were especially aggressive or difficult. When I've given talks at a conference, it was as an extremely young-looking (if not especially young) grad student, so I didn't have too many people trying to trip me up.
One thing about dealing with drillers and other contractors is that it forces you to deal with questions you may not have immediate answers for. If you get defensive or say something totally and obviously (in hindsight) wrong just to say anything, then you have to deal with the consequences - extra time and effort, more miscommunication, and worse, bad data.
After going through lots of pre-bid meetings, initial orientation/safety meetings, and discussions with clients/regulators, I had lots of practice working through the implications of a question with a big audience waiting for an answer. And lots of practice saying, "hmm, I didn't think of that. I'll have to check and then get back to you"!