Buying crypto with Card is Painful.

Why do all crypto marketplaces show different exchange rates for card payments, and then, after you register and complete verification, they drop the rate by 4-5% for no apparent reason? How do they justify offering only 900 USDT for a €1,000 card payment? That’s equivalent to a 15% fee. Can anyone recommend a crypto exchange I can use with a bank/credit card or Google Pay that has low fees? Like %3-4 at most.