It's going to be interesting here, so here's a bit of guidance.
Promotional posts by new users are generally suspect
If a new user arrives to the site and begins immediately promoting a product or service, there's a very good chance that they've come here for the wrong reasons, and should probably be destroyed. Flag these as spam.
However, if they've got some good contributions to their credit as well, it might simply be prudent for moderators to contact them and let them know excessive self-promotion is not tolerated. If unsure and you think there might be a real user behind these posts, flag as other and explain, otherwise flag as spam.
If they've actually answered the question, then assume it's a live human being on the other end - mods should start a dialog before doing anything destructive.
Promotional posts by established users are harder to sort
If a significant number of a user's posts do nothing but promote their company, they probably need to have a conversation with the moderators. This is especially true if promotional posts only tangentially answer the question at hand. Flag this as other and let the mods know specifically what you saw, where to look, etc. Please don't go through the user's profile spam-flagging a lot of things, this will lead to an enormous, emotionally-draining explosion later.
Obvious spam is obvious
If the question is about transferring money between countries, for instance, and you see low quality mostly-link answers, flag as spam - enough flags on these automatically delete the post, and feed the spam system.
Pay attention while reviewing suggested edits
Most of the spam that Stack Exchange sees across the network comes in the form of anonymous suggested edits. Watch out for links being introduced (they sometimes use strange formatting to try and hide them), and links being changed. Reject edits that look like spam as spam - this feeds the spam system to keep them from doing it again.
Actually, pay attention everywhere
We're going to get questions where folks are going to be giving honest testimonials of something they've used. Just make certain you've read the question the answer is attempting to answer, and involve a moderator if you're ever uncertain.
After a few months, the most active core community here is going to get a pretty good sense of what's legit and what isn't - I do see the same sort of guerrilla marketing onslaughts happening here as we've seen on Travel in the past. Keep your eyes peeled, but make sure you act with confidence.