If the price of an item you've purchased has changed, you can claim the difference using Price Protection. Details & list of cards that offer this perk.
Price protection allows you to claim the difference of an item you've purchased in the case that you can find the item somewhere else for cheaper within 60 days. For example, let's say that you purchased a dining set from Walmart for $800. A few weeks later, you see that same dining set being sold by Costco for $700. You can claim that $100 difference as long as you purchased the dining set using a credit card that offers price protection.
While there's no limit to the amount of times you can use Price Protection, there is a limit to how much you can get back per claim and how much you can get back overall per year. This will depend on the card holder, but most price protection programs max out at $1,000 per year. The amount you can get back per claim is usually around $500, but it is lower for some cards. If you plan on utilizing price protection, be sure to keep your sales receipts handy as you will need them when filing a claim.
There's not a lot of credit cards that offer price protection and most of the cards that do offer price protection typically aren't the ones that you see on the best credit cards list (unless you're looking for the best cards for price protection). While these cards will typically earn you a low return on your spend, the fact that you can get $500 to $1,000 back per year significantly makes up for the lack of rewards.