This might sound like a given, but it looks better if you can do your own photo shoot in your own style - it goes back to the word of mouth marketing. If you are the one wearing the product or have styled the picture yourself, it is more genuine and more likely to lead to a sale. @victoriama9 is a great example of this - it’s clear in the images that it’s her wearing the outfits and not a photo from the brand.
I would have one partner create a separate page/contact form specifically for the advertiser – so only people who see that contact form are people who were referred to by the advertiser. The advertiser would use that page as their outbound link. I know you can track outbound clicks in Google Analytics events and Contact Form conversions (usually through most contact form plugins) but that is the best way I think. Never done it, but this is how I see most affiliate programs like that work.
Very useful info, and thanks for the heads-up about Etsy not allowing affiliate links on Pinterest! Have you ever tried advertising on Pinterest, i.e. paying Pinterest to promote your pins? I was wondering if that could be lucrative with affiliate marketing, where the margins are always lower than when you have your own product to sell. I’m also wondering if it would be lucrative to advertise on Google, Facebook and Youtube (found this guy who supposedly made a lot of money that way – https://moneytestimonials.com/crestani-free-webinar/ ). I’ll probably do my own experiments with this but if you have experience in this area I’d be very interested to hear about it!