How about an option for any user of the forum with over X posts (say, a couple hundred) and lasting accounts (over a month) to be able to flag a post as spam and temporarily render it only visible to moderators?
Spamming is only meaningful if the spam stays visible for more than a few minutes and that happens only if the spamming comes in faster than the moderators can remove it. With a couple thousand people having the ability to render spam nonvisible with a click, the boards should stay clear of spam.
Limited to long-time users for accountability, the option is unlikely to be abused and however cheap it is to make spam, if it can be rendered ineffective by the first guy who sees it it will still lose people money.
Besides, how many times have you guys been browsing a threat or forum and happened upon annoying spam before the moderators could remove it? The ability to vanish it instantly would be quite cathartic.