Is anyone familiar with the rules, if any, relating to "write downs"? I use the term to mean the situation where one purchases a ticket, say an "L" fare basis, then the carrier subsequently lowers the "L" price. For example, Delta recently lowered a round-trip "L" fare for EWR-ATL from $193 to $183. To get the cash difference, you have pay the $75 penalty -- which usually makes no economic sense. The carrier will, however, (and you sometimes have to push) give a "write down", giving an MCO coupon for the difference which can be used on future travel on the carrier. [NW's MCOs can be transferred once!].

Is there a requirement that the carrier do this, or do carriers do this as a marketing tool to try and retain loyalty. If required, what/where are the applicable requirements?

Thanks.