Check a cut-out's edges in 30 seconds

1. Add a solid colour fill layer under the cut-out, in a bright colour that clashes with the original background.
2. Zoom to 200% on the hair or the softest edge.
3. Switch the fill between bright and near-black. Halos show up against one or the other.
4. If you see fringing, try Enhance Edge or Decontaminate Colors, then repeat the check.

Keep the fill layer hidden in the file. The next person to edit it will thank you.