I concur, leave framing to the buyer. The artwork is not the only consideration, but the space in which it will be displayed. You can't anticipate that. I have walked away from framed art because I was unwilling to pay the markup for a frame I knew I would have to replace.
Painting the side edges of a stretched canvas is nice, if you want to give the buyer the option of hanging it unframed, but do not intrude on image area. They will matte it themselves if they want it matted.