Is there a handshake agreement that copyright was transferred? Do the NFT auction sites say anything about this? What if the seller says "Oh, you thought I was

Is there a handshake agreement that copyright was transferred? Do the NFT auction sites say anything about this? What if the seller says "Oh, you thought I was selling you the copyright in the thing the NFT represents? I don't know how you got that idea, I never said that! I just sold you the NFT, that's it." Do people buying NFT's actually get some kind of agreement that the seller owned the copyright in the thing represneted and sold it with the NFT purchase? Real questions, I don't use these things!