Dealing with cheaters is always tough. If the school is notorious for it, nobody is going to fault you for questioning a shot or two. Don't make a show of it, just handle it quietly if you feel somebody is overlooking a stroke or something because it could be just that, honest oversight. Talk to them and like Grndslmhtter said, mention it subtly by suggesting they maybe forgot something.
As far as the less etiquette inclined players, the most I think I can offer is to say....that happens. From high school to the 65+ league you're likely to find guys that don't always give the same respect as maybe they should, but that happens. Keep the golden rule in mind, treat them with the same etiquette as you would like to be treated. If the things they're doing are getting on your nerves and affecting your game, bring it up to them. If they keep it up, talk to a coach or ref.
Play your game and you'll do fine. Good luck out there and definitely keep us updated.