The graphic summarises the affiliate marketing process. You can see that the when a visitor to an affiliate site (who may be an online publisher or aggregator) clicks through to a merchant site, this prospect will be tracked through a cookie being placed on the visitor's computer. If the prospect later transacts within an agreed period, i.e. usually 1, 7, 30, 60 or 90 days, the affiliate will be credited with the sale through an agreed amount (percentage of sale or fixed amount).
Affiliate marketing is also called "performance marketing", in reference to how sales employees are typically being compensated. Such employees are typically paid a commission for each sale they close, and sometimes are paid performance incentives for exceeding objectives. Affiliates are not employed by the advertiser whose products or services they promote, but the compensation models applied to affiliate marketing are very similar to the ones used for people in the advertisers' internal sales department.
At the end of the day, I have two things to say. First, neither option is better overall than the other. It all comes down to how much effort you put into it, what connections you make, what you’re willing to invest, and the fickle vagaries of luck. Second, absolutely nothing says you’re limited to just one or the other. You can always build a dropshipping storefront and augment that income with affiliate marketing. No one can stop you but your competition and your own lack of ambition.
Unlike most offline marketing efforts, digital marketing allows marketers to see accurate results in real time. If you've ever put an advert in a newspaper, you'll know how difficult it is to estimate how many people actually flipped to that page and paid attention to your ad. There's no surefire way to know if that ad was responsible for any sales at all.
This is the #1 mistake affiliates make with email marketing. While it’s great to have a list to sell to, you don’t want to be selling all the time. Break up the stream of email sales offers with some content. Aim for about an 80/20 split. That would be four straight emails that give great content to your reader and then one email of take, which is the selling part.