I've set up ecommerce sites quite a few times and it was honestly 1 to 2 days of "work", install + configure and then the rest was customization which clients pay for and are patient for. We were ready to sell product within a day basically and then iterate from there based on client needs.
I guess I wasn't clear enough in making my point: Wordpress + Woocommerce can be setup very quickly and with minimal fuss and they can be as heavily customized as you want and rival whatever plugin-heavy Shopify sites are out there.
Someone who knows how to do all of those things, already knows that they know how to do all of those things. Nobody who uses a one-stop-shop like Shopify is duped into thinking it's something revolutionary. Either it's not something they know how to do on their own, not something they think is worth the trouble to do on their own, or not something they could afford to pay someone like you to do.
It's not revolutionary, but even with the stated two days of work in the original comment, you probably are spending a couple years worth of dollars compared to just using Shopify ignoring the time to find said developer, maintain the relationship if something goes wrong, etc. if you are just trying to get an idea off the ground.
There's also a %tage of sales where the 'build vs buy' argument makes sense in the other direction. Obviously, most sellers of physical goods have better reason to focus on growing revenue and promotional activity, not cutting costs. That break-even point (I think) is some where around $250K/yr revenue, but that calculation depends on margins and the relevant industry matters (from a future planning perspective).
I guess I wasn't clear enough in making my point: Wordpress + Woocommerce can be setup very quickly and with minimal fuss and they can be as heavily customized as you want and rival whatever plugin-heavy Shopify sites are out there.