This is not a great approximation. In the UK you can assume almost every person has a payment card that works on the internet (debit and/or credit). In Poland on the other hand, the number of systems gets silly (https://m.lot.com/us/en/payment-methods-on-lotcom)
In Poland you can assume almost everyone has a debit card that works on-line.
WRT. your number of paying systems, note that there's exactly one Polish payment system there - DotPay. Every other system there is to support other countries (not surprising, given that you've picked up the site of the national airline).
There are outliers with a strong preference for cash, despite either owning a card and/or having almost no restrictions on acquiring one e.g. Switzerland is neither an EU nor EEA member, but is part of the single market; the Swiss seem to prefer cash over cards primarily for privacy reasons.
Credit / Debit cards are the same thing online. We, as is USA people, use the terms interchangeable often. I'm going to guess that most EU people have some form of banking card. So we will continue to assume that people have a form of payment other than cash.
No, they are not. With a credit card you can pay by entering the card number, expiry date and CVC. With debit card you can't do that. The payment must go through your bank. It's a completely different payment flow.
It depends on the debit card. I have both Visa Electron and Maestro, and they have 16 digits, CVV number and they behave like a credit card with 3D Secure when doing online purchases, while taking the money from the account right away.
There's also multifunction credit and debit cards (Mastercard and Maestro, or the Visa equivalent). They are branded like credit cards with a tiny Maestro logo on their backside, so I had to explain and ask the cashier in a grocery store in Amsterdam to try it as it would magically work as a debit card.
No idea what you are talking about. I have a VISA debit card and I pay the same way that I pay with my credit card. It is not a different payment flow on my end.
Not only do both have completely different payment processing workflows, but there's another key takeaway:
With a credit card the money going out is the issuer's. If you have a compliant or need to handle a charge, it's not your neck on the line.
With debit? Once the cash is pulled it's pulled. Yes they have protections as well, but while you're fighting with your bank to get your money back it's gone.
This is not a great approximation. In the UK you can assume almost every person has a payment card that works on the internet (debit and/or credit). In Poland on the other hand, the number of systems gets silly (https://m.lot.com/us/en/payment-methods-on-lotcom)