I worked a 36 hole US Amateur qualifier at Roddy Ranch last summer. For much of the second round, I was stationed at the 14th (I think) hole. The hole is a long par four, with tee shot over a hump then downhill to a blind landing area. There is a spot near the bottom of the fairway which serves as a collection area for long drives. Sure enough, two balls came to rest touching each other. I told the player whose ball was closer to the hole to mark his position, move the mark, then replace the ball after the other player had played. The obvious question arose: There would be a divot where his ball was which wasn't there before. I was certain the player was entitled to the original lie, but was unsure whether it would be a placement or a drop.
We were at the bottom of the course, and out of radio range due to topography. I tried for a minute to get a response, then discussed it with the player. He was likewise unsure. We agreed that he would drop, choosing to err on the side of caution. He would likely not be disadvantaged, since there was a pristine area right near where his ball originally lay. His ball ended up in as good a lie as the original, and he almost pitched in for eagle.
On my way back to the clubhouse after the last group was through, I ran into a certified rules official. I explained what I'd done, and the official told me I'd done the right thing, which made me feel better. Before I got to the house, however, the official called me back and said it should indeed have been a placement. Here's the rub: If the ball had been in a divot, and the first player to play made a bigger divot, and there was no similar lie nearby, he would have been required to place it in the now deeper divot.
What did I learn? When in doubt, ask, and even if you get an acceptable answer, ask again, as it may not be right. Kudos to the official I asked for getting double-checking and getting back to me.