Most of them are framed in gold, silver, or black metal with single or double white mats.
The mat sizes are usually 16 X 20 or 22 X 28 inches with glass or Plexiglas and foam core backing of the same size.
This framing is usually readily accepted in art shows. I feel the painting is the subject, not the frame. These frames are not expensive and so my prices can be more affordable by more people. If one wanted to re-frame they could take it to a framer or could find one in any ready made shop because the sizes are accessible. I do have a few that I have done that way.