When the document to be scribed is a bill of divorce, the husband pays the cost of the scribe -- with a rational for why he does, and also why that responsibility was later given to the wife. Plus, in other pairings for documents that need writing, the determination of which party pays (eg - debtor vs. creditor, seller vs. purchaser, and so on). Plus, the worry about the selfish trait of Sodom... Also, the risk of exchanging partial payment for the document, which can allow for the debt to still be in play in full. So the Gemara details the need for certification of a document, often enough via the courts.