So far as I know, tipping is not generally done at trap events. At Maringo, we had the nicest young lady pulling/scoring/trapping for us on several events over three days, and I quietly slipped her a $20 after we finished our last round. That was an unusual circumstance, and I never mentioned it to the other guys on my squad.
At our local shoots the club members do the scoring, me among them, and occasionally someone will shake my hand and say "thanks". I always complement and thank the scorer, and the friends on my squad. On the way out, I thank the guys behind the desk and the folks in the kitchen at the host club for their hospitality ...especially if they're serving those wonderful dirty 'ol country ham sammitches.
For sporting clays, after a round of 50, we tip the trapper $5 each.
We had a decent day last Friday here in the frozen wasteland of MN, made it into the 30s. Poor highschool girls out pulling and scoring all day, I shot 4 or 5 rounds and figured I should leave something. They did a great job and never once complained about the cold or not being able to warm up. Usually I don't leave anything, but they really earned their wage that day.
I don't know when I'm allowed to or not, so I don't. I have brought lunch and sodas for some that I personally know and care about. I have also made cookies, pies, and cakes and put them in the clubhouse for them.
I've been on squads where some of us saw a shooter's target break while one of the shooters couldn't see the chip fall from his/her angle. I appreciate the trap help very much, but I am always wary that another shooter could accuse me of having given a bribe.
Our club is run by all volunteer help. Also due to insurance regulations we can not let anyone under 18 to load the traps. What we do is along with our youth program we let the youngsters shoot for free as long as they keep score and help clean up at the end of the shoot.