If you look at the SpamAssassin wiki you can find a list of products that are based on SpamAssassin that your billpayers can feel happy paying for while not getting access to all the source code. That way they can continue to be blissfully ignorant suckers and you can still use SpamAssassin. (I don't mean to reflect on the commercial products, only on the apparent attitude of your bill payers).
In some cases the source is open, so you can still tinker. Open is not incompatible with commercial. As jokingly mentioned on the Users list, someone could burn a CD of SA, slap on a pretty label, and add a price tag to make the suits happy.
