How often does anyone see the need to have to disclose the amount or percentage of down payment in a closed end ad?

This would apply only in a credit sale transaction which by definition is a transaction in which the seller is a creditor.

We’re a creditor but not a seller.

Is this disclosure most likely seen when advertising sale of foreclosed property?

You can mention the term "down payment" or "20% down" in an ad without it being considered a "down payment" as defined in the regulation, as long as you are not a seller in the transaction. For a bank, credit sales most often arise when selling foreclosed real estate or other repossessed collateral (automobiles, for example).

Thank you John