Suppose a guy has a share in his family's business. Then:
1 "He sold his share of the family business."
2 "He sold off his share of the family business."
3 "He sold out his share of the family business."
Dictionaries suggest that they are vaguely the same and that "sell off" and "sell out" may sound more poetic. But how are they used by native speakers?
I would say he "sold" his share of the family business, "sold off" some of his shares in the family business, and I wouldn't use "sold out" at all in this context.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.