It's a metaphor. It's the kind of thing you'd say after a job interview, or any situation where you're trying to impress or "sell yourself." To sell oneself in this case doesn't literally mean to sell yourself into slavery or something. Instead, imagine a salesman trying to sell a product and persuading the potential buyer by going over all the positives and good points of the product. This is kind of what you do at a job interview: you're trying to persuade the other person why they should hire you.

Thank you...

To sell oneself can mean to try and make yourself appear really good/attractive to others. Literally it means to sell your body in exchange for money.

It's a metaphor. It's the kind of thing you'd say after a job interview, or any situation where you're trying to impress or "sell yourself." To sell oneself in this case doesn't literally mean to sell yourself into slavery or something. Instead, imagine a salesman trying to sell a product and persuading the potential buyer by going over all the positives and good points of the product. This is kind of what you do at a job interview: you're trying to persuade the other person why they should hire you.