Sorry jiffr.
There is NO law for this in Maryland. Certain stores may offer you a refund in the difference in price if THEY decrease their price in a certain amount of time (usually 2 weeks to 30 days). This is the individual store's or chain of stores' policy, nothing to do with the law.

Also note: some credit cards do offer a price guarantee. If you can prove that the price decreased in a certain amount of time (usually 30 days after purchase), they will refund the difference. I never tried this before but it may work with a airline ticket without having to pay the change fee charged by the airlines.

If there were such a law it would be the state effectively saying that all sales must be at least 30 days long. No merchant would put up with such unwarranted intrusion into a merchant's perogative.

Store policy I believe. I have known people that have made purchases and right afterwards, day or two later, saw ads that the same merchandise was on sale. They have taken their receipt back and have received a credit for the difference. I don't know if any of our stores do that anymore however.

Jiffer,
Your paint story was funny.

I used to not fly much and thought a plane ticket had a "price". I also used to think you could use Dividend Miles to get a ticket whenever you wanted to fly. What an education I have gotten over the last few years. Took a lot of hours to get a grip on the ticket game. I think I have it figured out but next time I go to get a flight, I am sure I will learn more - the hard way.

The paint story reflects a lack of understanding of the various prices of what would appear to many to be the same ticket.

Each fare has a list of rules attached, but it appears that many of us don't bother to read those rules, so we don't know what we are really getting. Just as a simplification, some of the terms that can vary and lead to a different price are how far in advance the ticket is purchased, how many days the trip will last, whether there will be a saturday night stayover, whether the fare is refundable, and whether the trip will earn frequent flyer miles. I'm sure there are more, but I'm writing without doing research to find out the others. And of course, the prices also change as the airlines work their revenue enhancement magic, but those are closely guarded secrets.

I think most of us are unwilling to put in the time necessary to research and understand this arcane subject, so we just complain. I think usually fares don't go down far enough to make pursuing the issue worthwhile, and who among us would send more money in when the prices increase.

The OP was fortunate to be in a situation where there was a drastic fare reduction, and to come across a ticket agent who made it work for her.