<p>Could Magneto be the one for you? I am satisfied with it, I haven't looked into Squarespace too much though.<br /></p>
The reason for me sticking with Magneto is in the cool extensions I was able to add to my website. The one I liked the most is an auction extension from https://amasty.com/auction-for-magento-2.html. It's so cool, adding that option to your store can get you more profit. The cool thing is that it is easy to do because it's set up already, and adding it would be the easiest thing. I am not sure if Squarespace has something like this.