There is a solution though, don't buy secondhand unless you KNOW the part is legit. To me the savings aren't worth the knowledge that some smooth talking **** is making a living out of nicking peoples bikes.
Completely shut down the used bike parts market?
Good luck with that plan...
Forks usually have a serial number don't they - is it worth us documenting and storing them alongside frame numbers.
Now that is an eminently sensible suggestion, but just how much chance is there that the number on your forks is fully traceable via manufacturers, OEMs or Distributors? anyone ever tried?
At the end of the day any half cognisant thief will know which parts have more chance of being traced and which don't, Brakes, Cranks, Dropper posts, Mechs/shifters, Wheels?
All desirable/sought after items, relatively portable, probably quite tricky/impossible to trace, you don't need to flog the frame/forks to turn a profit...
The OP linked Thread says it all, other than the one bike they could prove was stolen, which the suspect claimed to have bought in good faith, they couldn't link any of the other stuff in his Garage to reported thefts, from the sounds of it 10+ bikes worth of higher value stripped parts and frames... Thats a few grands worth of kit.