Royalties are typically 2.5% to 10%, set by the project. Crucially, the erc-721 standard cannot enforce payment on a plain transfer, so they depend on marketplaces choosing to honour them.
That dependence collapsed when zero-royalty marketplaces gained share, cutting creator revenue sharply and changing the economics many projects were built on. Some projects responded with transfer restrictions, which reduce fungibility across venues.
Example: selling at 5 ETH with a 7.5% royalty and 2% marketplace fee nets 4.525 ETH. On a zero-royalty venue the same sale nets 4.9 ETH, which is why sellers migrated and why quoted floors across marketplaces can differ.
Related: nft, nft-floor-price, erc-721, wash-trading-crypto