This just gave me the idea to make a website where you put in a transaction ID and it gives you a 'taint score' (just like those other blockchain analysis services), but this score is simply always 100%, with a nice green background and informative text saying 'This UTXO is wonderfully clean; it is yours if you have the private key to spend it and you can send it anywhere you like.'..

Then whenever someone is accused of having dirty coins, they can pull up a screenshot of this site and it will be 'word against word'.