Not sure I'm buying it.
Dr. Schultz goes through so much bullshit to get to the point where he is able to free Django's wife. All that travel, time, energy, acting, etc.
Calvin Candie becomes wise to their little scheme and how does he react? Does he kill them? Torture them? No, he simply forces them to comply and abide by the terms of the contract they AGREED to... $12,000.
Even after the deal is done, after all that disrespect and backtalk from Django, how does Candie respond? He continues being a very polite and hospitable host by offering them drinks and cake, handing over the proper paperwork for her freedom, etc.
Then.... Dr. Schultz just snaps because Candie insisted on shaking his hand? Huh? Even if he wanted to kill Candie, it seems like he would have left the house and planned it better. Or maybe he should have shot his henchman with the rifle, taken his gun, then shot Candie... something other than a certain suicide mission to take out his single shooter spring-loaded Derringer from his sleeve.
I'm a butthurt faggot because of the ending.