Topper's fee page is short on numbers. It states that the fee depends on the payment method you pick, that a minimum of $3.99 applies to every transaction, and that the blockchain network fee is separate and paid to the network, not to Topper. There is no table listing a card percentage, an Apple Pay percentage or an ACH percentage. The rate is calculated for your order and shown on the confirmation screen, which is where reviewers say they first noticed it.
What those reviewers report is a wide range. Some found the rate acceptable; others cite card fees well above 5%, and a few name 7.4% on a debit card. The spread between them likely reflects the payment method, the partner app and the order size, since the $3.99 floor dominates small orders. Selling through Topper, where a partner enables it, carries its own fee. Because Topper never holds your coins there is no withdrawal fee in the exchange sense; you pay the network fee to deliver them.
Anytime Capital prints its card pricing on the page: from 4% with the spread included on card, Apple Pay and Google Pay orders, one all-in number, with the amount you pay and the crypto you receive shown before you confirm. At Topper it is whatever the confirmation screen says, and the only way to know is to get there. The honest comparison is to put both checkouts side by side on the same amount and look at the coins that land.