How do you do it?
The more elaborate version of the scenario:
Non-heroic Mechanar with the humanoid 3-pulls at the start. 2 casters, 1 melee. Pally tank marks caster for trap and then pulls with a thrown shield. LoS is not too tricky, but the difficulty is compounded by the tremendous effort I have to put into getting the caster off the Pally before my LoS options are gone and before my trap expires. Aimed Shot takes too long...by the time it goes off the mobs are already on the Pally who is not positioned for me to use LoS. Nevermind that I pretty much need a crit on Aimed Shot to generate enough threat to get the mob to focus on me. Level 71 caster mob means if I try to stack hate on my pet with Misdirection and have pet draw mob into trap, my pet is dead before the process is halfway complete. That means more downtime to rez/feed/heal pet.
Seems to me like it was just another ignorant tank/marker, but I don't want to write it off as such if there's something more I could have been doing. I left the group before we had made it to the second room because it just wasn't working. (I actually had another Hunter lined up to replace me, but the tank who had lead to mark suddenly didn't have lead to invite them anymore. While the other Hunter was trying to figure out what was going on, he and I were chatting. I explained why I left (to include me feeling like maybe I just wasn't on my game) and I think he decided not to join the group after all. Two partial wipes and one full wipe in the first room of an instance is usually a bad sign.