Yes some of the largest Northern European banks.

https://trustly.com/en/

I loooked at their pricing page on https://trustly.com/en/pricing/ - not a single price is there. Come on guys...

If you publish any kind of price, that affects your negotiation options if you want to do individual pricing/haggling for each customer.

Also, a multitude of factors affect the 'true' price including various risk estimates of your company, and it would be counterproductive to say "factor X, as measured by Y, gives you a price increase/decrease of Z", as that would just result in gaming the measurement and misleading about the nature of your business.

All valid facts - then just don't call the page pricing. Call it "enquiry" or "contact" or whatever...

I think it's excusable for a relatively niche B2B service where there's likely a huge variation in the size of their customers. Price discrimination is hard.

Never heard of it. The README only link RFCs concerning PGP. I didn't find a draft of standards for protocol itself.