If you have a quest already completed can you use the console to go back to a certain stage? I have all 7 Theives Guild Larceny items....but the quest to sell them is complete, and I never did get to sell them to Delvin. This is a known bug. I am wondering if I can set the quest back to where I can go sell them to him so they can show up on the shelves.

I've not come across any console command that will. As a matter of fact, that is why you should always SAVE often throughout the game.
However, you might want to visit the Skyrim UESPWiki at "http://www.uesp.net/wiki/Skyrim:Console".

"Warning: Use console commands with caution! It is easily possible to mess up your game if you modify settings at the console. Even if short term the game functions normally, you may later discover that you have made it impossible to complete a quest and therefore you cannot proceed normally with game play; fixing that problem can then make new glitches pop up elsewhere. Create a permanent saved game before experimenting with the console. If you need to use the console to fix a glitch, try to use the least powerful command possible."
Good luck.

You cannot go backwards in a quest via comsole commands, only ahead. You cam use the commands to give you any item you may be missing out on due to a broken quest.