There is many affiliate marketing company on internet. Some of example is clickbank, SFI, amazon, or even local affiliate marketing program. Many people wanna be affiliate marketing but don't know which program is good? Before join to a program, you need to know :

1. Product Collection
Affiliate program which have a lot of collection of product is good. You can choose free many product option based on you research. If affiliate program have less collection of product, it can annoying. For example, you do a reasearch and find that stomach cancer is a niche, but in your affiliate program, there is no stomach cancer related program. That's mean you'll lose a chance

2. Commision Rate
Commision rate is the most important thing if you wanna join a affiliate program. We're as affiliater of course wanna appropriate commision for every sales we made. I ever hear there is a affiliate program offer 75% commision, but there is also bad affiliate only offer 10% commision, and of course 10% is not worth, avoid it.

3. Bonafide of the company
Of course you need know about this. Because you don't want to get scammed right? So, before join to a affilaite program from some company, try to search testimonial or payment proof. So, risk of being scammed is reduced

That's 3 point you need to know before joining to affiliate program company. Can you add more or give me some opinion? Thanks, hopefully my tips is usefull.