After reviewing Section 226.17(c)(1) {The disclosures shall reflect the terms of the legal obligation between the parties.}, the OSC makes more sense and provides the answers you need:
Section 226.4(c)(5)
1. Seller's points. The seller's points mentioned in ยง 226.4(c)(5) include any charges imposed by the creditor upon the non-creditor seller of property for providing credit to the buyer or for providing credit on certain terms. These charges are excluded from the finance charge even if they are passed on to the buyer, for example, in the form of a higher sales price. Seller's points are frequently involved in real estate transactions guaranteed or insured by governmental agencies. A "commitment fee" paid by a non-creditor seller (such as a real estate developer) to the creditor should be treated as seller's points. Buyer's points (that is, points charged to the buyer by the creditor), however, are finance charges.
2. Other seller-paid amounts. Mortgage insurance premiums and other finance charges are sometimes paid at or before consummation or settlement on the borrower's behalf by a noncreditor seller. The creditor should treat the payment made by the seller as seller's points and exclude it from the finance charge if, based on the seller's payment, the consumer is not legally bound to the creditor for the charge. A creditor who gives disclosures before the payment has been made should base them on the best information reasonably available.
The pivotal question is always - what does the credit contract say? Side agreements have no bearing on Reg. Z disclosures unless they become part of the credit contract in one way or another.
Notice how the OSC handles seller's points. To be excluded from the FC, these points must be "imposed by the creditor upon the non-creditor seller." Imposition occurs by contract--the seller has entered into a contract with the lender, agreeing to pay points as an inducement for the lender to provide credit to the buyer. Unless that contract is amended in such a way that the borrower becomes legally responsibility for paying these points, they are excluded from the FC. Again, remember that side agreements between the seller an buyer have no impact on the Reg. Z disclosures. This would include a seller/buyer agreement that the sale price would be jacked up enough to cover the extra cash the seller will need to pay the points.
"Other seller-paid amounts" follow the same Reg. Z coverage rules. If the credit contract says the borrower is responsible for various fees, then these fees are included in the Reg. Z disclosures (as applicable.) Even if the seller (or anyone else, for that matter) steps up and agrees (side agreement with the borrower, only) to cover the cost of the fees, Reg. Z requires the fees to be included in the disclosures. Three-party agreements are different. By adding the lender to the agreement to transfer responsibility for payment of the fees in question, you have effectively amended the credit agreement. Now that the legal obligation between the parties calls for the fees to be paid by someone other than the borrower, "the consumer is not legally bound to the creditor for the charge" and the fees are excluded from the disclosures.
Remember - the real question is not "who pays the fees", but rather, "who's contractually liable to pay the fees."
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...gone fishing.