An econ platform that donates a % of proceeds to pre-selected non-profits?

I'm often skeptical of claims about stores donating proceeds of product sales, especially from small (less scrutinized) businesses. It's a shame because I assume a lot of people would want to support small businesses and charitable organizations simultaneously, if it was all transparent.

I was hoping to find a well-designed e-commerce platform specifically for that purpose, that I could sell custom products through, but not coming up with anything that isn't sketchy looking in of itself.