My company uses Stripe among others. We do on the order of 8 figures of transactions over all our payment channels. Not a whale by Stripe's standards, but not nothing either. We also have enterprise agreements in writing and signed contracts with all of them. It wasn't necessarily an underwriting process as far as I know, more of an enterprise software licensing agreement. But either way, they are obligated to provide services under the terms of the contract. The terms include some commitment to future use and get us at least a smidge of discount off their fees. As much as startups love buying services with transparent pricing where you just pick a service level and plunk down a credit card, when it's business critical, just call their biz dev team and ask for a contract.
Honestly, idk. It at least gives you grounds to seek redress via legal channels in the case that you do lose business. I'd hope that the threat of legal consequences makes them be a little more deliberate in their actions.
