Marketplaces are good places to sell because people come there. The visitors may not find you in amongst all the other marketplace sellers, but at least they are coming to the marketplace.
Selling from your our own site means you have flexibility and the possibility to stand out and look better than the competition. But then you might struggle to get people to come to you at all. How do they even know you are there?
So it’s a numbers game. The question is, is it better to be in a marketplace where you have a hard time making your design stand out or is it better to have a design that stands out but struggle to get people to come to you at all?
Shopify and all the other SAAS providers are the worst of both worlds in some ways. You build your site on their platform, but then you are on your own, as anonymous as if you had self-hosted your site.
Instagram and FaceBook shops seem like a good idea, but are they like crashing the party for people who are looking to socialise, not to buy?