Depends on the interest of the buyer.A painting which I dislike may be liked by u.So,beauty lies in the eyes of the beholder.

Who painted it

You should have love and appreciation of art, to know the dating, the artist and the nationality., if you know these and it they are famous., then you could price it accordingly., it also depends on where you are going to showcase the art., you have to pay for the place and the person who showcases ur art.
If the artist still lives the price cant be set as high then if the artist has passed on. if that particular piece or art has been showcased before in any famous gallery or museum, you can hike the rate too., even-more-so if the art has won any prizes, grants or honours., u can price the art based on the position the artist has held when he completed the peice for eg.teacher, lecturer or writer, the pricing could be determined even as to where the art was menitoned in publication., books, catalogues etc, the more it is mentioned anywhere, a better price can be asked., then comes placing the art.