The problem is that when John converts to Bitcoin he may receive Bitcoin that has a criminal history attached tainting it. That taint may prevent John from usin

The problem is that when John converts to Bitcoin he may receive Bitcoin that has a criminal history attached tainting it. That taint may prevent John from using his Bitcoin at certain places or exchanging it elsewhere. It may also mean the US decides at some point that his Bitcoin should be seized due to that criminal history. How does John know he is getting Bitcoin with only a clean history?