A cart guy brings out your golf cart for you, they handle your clubs, they clean your clubs at the end of the round, then they clean the cart and return it to the cart barn. They’re doing something for you, so you need to do something for them. Most of these guys make a small wage and depend on tips for their salary.
Even if they get a couple of dollars, that money adds up over the course of the day. In my opinion, the general rule should be about $5 per person or $20 for a foursome. Feel free to tip more if you feel so inclined. When you tip these guys, word spreads. You’re going to get better service and you’ll be liked more around the course the next time you show up.