Punishing spammers?

The actual asshats who provide the mailing services are greasy, slimy, sleazy and difficult to get at. But what about their clients< the people and companies actually selling the products on whose behalf the spam is sent? Why can't we go after them? Since they have to have a physical presence in order to accept payments (and potentially make shipments), the piles of moron shit must be accessible. Credit card companies can be pressured to rescind their accounts. How about it?