One con I can think of is that you don’t get to establish any sort of relationship with your customers. When you’re selling someone else’s product, there’s no chance for you to connect with them on a deeper level like you would if it was your own creation.
I personally feel that a lack of relationship with customers will lead to a lack of trust over time as they realize just how little they know about who they are buying from. This could cause them to be wary every time they need to buy something in fear that something similar might happen again.
Of course, affiliate marketing isn’t right for everyone but just keep in mind that depending on what type of relationship you want to have with your customer or clientele, there are ways to make it work.
Also, my one word of advice: test!
See what works best for you and run with it! It doesn't matter if it's an established company or a side project; find out which platform gives you more personal satisfaction by seeing what gives off more positive outcomes.
There are many variables involved so play around with some things and see what fits you best. Just remember that these cons don't only apply to affiliate marketing; they apply to most other forms of business as well (unless you're working directly with people).
However, if done properly, affiliate marketing can help small businesses succeed in various niches without having to worry about overhead costs because affiliates usually handle their own overhead costs (advertising) while gaining a greater percentage per sale than paying advertising fees typically cost.
Hopefully, now that we've explored some pros and cons of affiliate marketing, it'll give us both insight into whether we'd like to pursue affiliate marketing more seriously or not.