He offers to rewrite the name with that of the buyer.

And while the paper "belongs" to him, in reality that paper is a credential issued by Harvard, and the source of truth for credential holders is Harvard, not the holders/subjects.

All colleges maintain lists of credential holders.

An attempt to verify the ownership and subject of the credential- which happens quite often, many mid to high level employment offers, all background checks, etc, perform this verification- using the buyer's name, fraudulently rewritten on the piece of paper- will fail.

Issuing fraudulent credentials of various kinds and advertising them as valid...is fraud.

And if you don't think so...I've got a bridge to sell you.

Cheers.