* Yes, Stripe take a fee and that sucks, but you don't have to. Shopify had $0 monthly costs at launch. Obviously now they can charge what ever they want
* You just launched, putting some fake discount on seller fees just seems spammy. Like a 30$ product with a $60 + 50% off label. Seller fees were never 3.9%, there is no discount.
I think this is a great area to focus us. And you, or someone else will end up taking over the market. But I think whoever it is will give their product for free, or at a loss, for at least 6-12 months.
Before you figure out why people are/aren't signing up, why not see if price is the issue? Once people are locked in/love your product, raise the price as much as you'd like