Most people assume that if there is no rogue in the dungeon group, then any locked treasure chest within the dungeon is unlootable. "It's locked. Keep pulling!" I'm not sure why this is a common belief, but I always use it to my advantage. We as auctioneers are often profitting off of other players' errors and ignorance, and this is another oppurtunity.
If you are dungeoneering in a guild group or with a group of friends, then you probably use your lockpicking skill to open any locked chests. If you are in a PUG dungeon group, do you use your lockpicking skills? I only do if it is a quality group and we are planning on running multiple dungeons. If not, I ignore all locked chests within the instance. Why? Being the greedy and evil goblin that I am, I want to keep all the chest's contents for myself. I go back through the instance after the dungeon group disbands and claim all of the chest's goodies for myself. These random PUG members may never cross your path again so you don't really owe them anything. You way remember back during Hallow's Eve when I discussed this tactic briefly for claiming all the scarlet monastery chests for yourself.
3 Ways To Ninja Locked Chests
1) Rogue - "Sorry my lockpicking skill isn't high enough." Then go pick the lock once everyone leaves and collect all the gold and items.
2) Blacksmith - No one needs to know that you are a blacksmith or whether you have blacksmith keys on you or not. Use those blacksmith lockpicking skills after everyone else leaves. You do carry keys on you right?
3) Engineer - Just like blacksmiths, engineers can craft seaforium charges to open chests. Backtrack through the dungeon and collect those locked goods waiting for you in the empty instance. Bonus if you use a speed boost with your engineering gadgets to get to those chests.
Just remember to have the dungeoun group clear out any mobs near those locked chests so you can return to the safely when you are alone.