1. Expect not to be paid for all of your sales. This is especially true if you're doing CPA marketing. Furthermore, expect that many merchants/vendors will not respond to you when you send them emails asking why you weren't paid for a particular sale.
2. This isn't for people that are lazy and it's not get rich quick easy money bs. You need to work and work hard if you want to be successful in this business
3. If there's a dispute between you and a vendor expect the marketing network to almost always take the merchant's side. It boils down to economics. Affiliates are easily replaceable. Vendors not so much.
4. Most of the affiliate marketing gurus out there don't make as much money as they want to lead you to believe.