In the case of cost per mille/click, the publisher is not concerned about whether a visitor is a member of the audience that the advertiser tries to attract and is able to convert, because at this point the publisher has already earned his commission. This leaves the greater, and, in case of cost per mille, the full risk and loss (if the visitor cannot be converted) to the advertiser.
If you are a music lover, it would be a good idea to promote it over books and even other products. All you need to do is listen to clips of a full album within a short period, say 10 minutes, get a good feel of it without you purchasing it and do a short review. If there is another niche you are passionate about, make sure you get a unique discovery about it. Of course, there are hundreds of thousands of reviews about these products all over the web but you need to make yours more unique to attract people to your site.
And another big reason? Cost. Most of the big Influencers work solely on a pay-per-post model, where companies have to shell out hundreds of thousands of dollars for a single Instagram post. Sure, maybe you’re Pepsi and you have that sort of spend. But we’re assuming most of you a) don’t want to spend anywhere near that much, and b) want to work with Influencers on a traditional affiliate marketing model (commission on sale). It goes without saying, it’s much more likely that micro-influencers will work on this model.