I believe that framing an artwork is akin to dressing up. Nobody should tell you how to dress up nor order you to wear a certain clothing item. Dressing up is a personal choice; so is framing an artwork.
The artist may suggest an appropriate frame’s color scheme by painting the sides a particular color. The buyer of the artwork should decide on his or her own how to frame a painting and what color to pick.
There are many styles of art and for every style there is a niche/target audience. Some people might disagree on the kind of frame that fits a particular artwork and that is absolutely fine, because every person is unique.
That’s my case of why an artist, having completed a painting he intends to sell, should never frame his artwork. The artist should leave it to the buyer to decide on the kind of frame that buyer believes suits his purchased artwork.