I am talking about a service for one person not everyone. I ask for someone's originating address, i type it into my dirty coin checker. I can choose to do business or not based on the results.
It's not that easy. The person can't be forced to send from a particular address. They could show you a clean address and send from a tainted address instead, and now all your coins are tainted (if you aren't careful).
There might be ways to mitigate or prevent this, but not with a simple blacklist service.
If the sender is sending from a shared walled (like an account on an exchange) it would be difficult to comply with such a request. If I were asked for my originating address(es) before sending a payment, I would take a pass for turning the transaction into a hassle. As bitcoin starts being adopted by the masses, I really doubt that the average non-technical bitcoin user could even figure out how to find the originating addresses about to be used in a transaction.
When case law eventually determines if bitcoin is fungible or not, in the case of "not fungible", bitcoin will likely fail as a convenient method of exchange, since it can be legally seized if it was ever used as part of criminal activity. If the law considers bitcoin fungible, your only legal obligation will be to prove that you acquired it in good faith and not as part of some criminal activity.