The verdict
If you are a creator selling ebooks, templates, courses or merchandise to an audience you already have, pick Sellfy. It gets you selling the same day, with secure file delivery included. If you sell physical products at scale, sell to businesses, or need your systems to talk to the store through APIs, pick BigCommerce.
The honest trade-off is control against speed. Sellfy has a ceiling on customisation, and moving off it later is real work. BigCommerce asks more of you at the start, but it bends further. For most small B2B teams, a catalogue with business buyers is a BigCommerce case. A creator selling their own work is a Sellfy case.