Do you have enough windows to let in natural light? Code requires 10% of the wall space as window space in a non-walkout to be counted as an occupied space. For example, if the finished section of your basement is 700 sq. ft., you need 70 sq. ft. of window area, or 2 5×7 windows. Hope this helps.

If your basement is finished with carpeting and most importantly a ceiling and is suitable as living space, then yes you can count it as square footage when listing.

Ask a real estate agent about it. A basement adds to the square footage whether it’s a walk out or not.