You have to argue your way through an army of outsourced supporters who are equipped with nothing but the public Shopify docs, until you get to a real employee who concludes it with a "sorry, but we can't help".
Some of my issues:
1. If you're not American, you will be forced to hand over 3% of your 80% revenue cut to PayPal. (Unless your MRR cut is >$30k)
2. Sometimes Shopify just kills features, which merchants and partners rely on. Sure, we get a notice that the API will change - but how does that help, when there is no alternative way to achieve the removed functionality? I was lucky enough to get through to someone who knew someone at the dev team, but the response was once again "sorry, you're not a priority".