Sometimes you have to wait a while. You can speed things up a bit though:
- Orange items on scanner are neutral, yellow are unresolved. So if you see any yellow triangles / squares on the edge of your scanner fly towards them until you're inside scanner range.
- Scan all craft, so their name changes in the Contacts list from "Sidewinder" to their name (so you can keep track of who you've scanned).
- Big haulers are rarely Wanted, Sidewinders/Adders/Cobras can be miners or Wanted. But I've never seen a Dropship or Clipper mine.. if you see one of those in your contact list, make a beeline towards it and scan it.
- If you're friendly with the security forces (as I am) then they show up green in the Contacts list, you can ignore those.
- Most craft you meet "up high" or "down low" aren't miners, since there are no rocks up there! Scan them.
- If you see a message in the Comms panel asking what you're carrying etc., that's inevitably from a pirate. As said above, you have to scan them before shooting though!!
- If you can see the name of a pilot in the Contacts list, but no bounty data (one way or another) that usually means you received a message like the above but missed it, so select that craft and scan them.
- And obviously, keep an eye out for weapons fire. Generally, if you see lots of lines-of-fire converging at one spot, that's there you'll find the Wanted guy.