Fastspring has a fraud protection system in place. Strip has not and does not prioritise it according to this quora comment by one of its co-founder. https://www.quora.com/How-will-Stripe-overcome-the-huge-loss...

Fraudulent chargebacks is bad, both economical and psychological. As an online seller it is part of life, but you want to keep it to a minimum, say < 1% of all transactions. I wholeheartedly support the sentiment of the OP, do not use Stripe nor do this in-house. Instead, use a payment provider with a proven fraud protection system, such as PayPal.