It seems to happen to me a lot, and more than ever recently! I went to do maintenance at my customers property and he had a tree company bringing down trees. It cost me thirty minutes windshield time! Sometimes I have been able to do the work, but unless we are both working solo, there often seems to be some negative interaction. I once spent three days working at the same property where a carpenter was building a deck, we both had two employees, and lots of materials, and it got crowded fast. I had to reschedule some stuff and ended up overbudget and behind schedule. The customer had screwed up the scheduling and it cost her.