She was lying to him. Margareta had never met this demon who had once been her, but she didn't need to. Demons lied. She knew that with certainty, demons were liars and manipulators. And Sam was falling for it.
"Cares..." Margareta shook her head again, the very idea of a caring and friendly demon, she was pretty far from any kind of Hunter, but she knew what she was talking about.
"I know in my time there were no tales of good demons, not one. Nothing to back up your words, but maybe in the centuries since...how is this demon that was me different, new"
He had been honest with her, foolish as he was so she decided to do him the same honour.
"Before I was here...I was ready to do it, to make the deal...I had been doing all sorts of awful things for Tatiana, her magic kept me alive and in return I would...do things. Cruel things, and then she came one day, and she asked to collect her due. In the form of my soul...I prayed Sam. I prayed so hard and I was sent here, to Castiel."