Consumers who think they’re getting a good deal by buying a casket at Amazon or Costco may end up paying more than they think in the end, advocates say.

As a recent Reddit thread reminded bargain hunters, Costco COST, -1.27% represents one of the cheapest options when it comes to purchasing a casket for a funeral. The thread garnered more than 1,000 comments, ranging from the humorous (one user commented, “I bet you have to buy a 3 pack or something”) to the heart-warming (another person wrote that it helped them with end-of-life planning for a terminally ill relative, saying, “you have no idea how much you may have just helped out me and my struggling family.”)

The warehouse club is famous for selling caskets — but it’s not the only place to shop for a bargain when planning a funeral. For instance, Amazon AMZN, +2.49% and Walmart WMT, +0.41% also offer competitive prices on caskets, not to mention the countless online retailers that specialize in coffins.

And while caskets were once unrivaled as the biggest funeral-related expense, people can lose some of the savings they found by buying through these retailers because of how funeral homes charge today. “Buying caskets from a discount retailer is not the primary way to save money anymore, and it’s not consumers’ fault,” said Joshua Slocum, executive director of the Funeral Consumers Alliance.

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Sales of discount caskets at retail stores, Slocum said, took off in the 1990s after the Federal Trade Commission ushered in the Funeral Rule, a set of rights regarding end-of-life-related goods and services. Prior to the rule, funeral homes could charge a handling fee if a consumer purchased a casket from a third party such as Costco or Walmart. Now, the rule bans that practice.

Nevertheless, to make up for those lost revenues, funeral homes have adjusted their pricing to account for the growth in third-party casket sales. In particular, funeral homes now charge a higher services fee. As of 2014, the median non-declinable basic services fee charged by a funeral home was $2,000, an increase of 37% from a decade earlier, according to the most recent data from the National Funeral Directors Association. During that same period of time, the median cost of a metal casket only rose 14% to $2,395.

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Another common strategy among funeral homes is to charge more for individual services such as the viewing and embalming and other items if a family purchases a third-party casket. (This practice is allowed based on a U.S. appeals court ruling, according to the National Funeral Directors Association.) As a result, it’s less of a given that loved ones will save by purchasing a casket from somewhere like Costco, Slocum said. “If you believe that will guarantee you will save money, you are wrong,” he said.

To make sure that a family will save by buying the casket through a third party like Costco or Amazon, Slocum suggested contacting local funeral homes and asking for a detailed listing of prices. Information regarding savings is also available through local chapters of the Funeral Consumers Association. “Combining a funeral home that has reasonable prices for services and then finding your discount casket is the best way to save money on a full-service funeral,” Slocum said.

When it comes to choosing the casket, Slocum had the following advice: “Regardless of where you buy it from, remember that caskets do only one thing: they hold the body.” With that in mind, consumers need to watch out for gimmicky advertising regarding caskets that preserve the body. Many casket descriptions will also reference the casket’s gauge of metal, which measures how thick it is. But the metal’s thickness only matters for anyone who might carry the casket and won’t make a difference once the casket is buried. Similarly, warnings regarding shoddy construction are designed to appeal to a family’s fraught emotions when planning a funeral.

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As for the choice of where to buy a discounted casket online, a casket from Costco can cost as little as $950 (with standard shipping included) or $1,230 (with expedited shipping.) Caskets from Walmart range in price from just over $1,000 to nearly $4,000. Amazon, meanwhile, had the cheapest option: A $791 casket available through Amazon Prime with free shipping.

People who buy a casket from a funeral home can expect a higher price in many cases. Slocum compared the potential mark-up on a casket to a $500 iPhone from Apple costing $1,600 when sold by another retailer. “Caskets are marked up much, much higher over their wholesale than most other merchandise is,” he said.

When buying a casket from a third-party retailer, it’s important to understand the terms and conditions of the sale — especially if it’s a lesser-known company. Third-party retailers are not required to abide by the FTC’s Funeral Rule, said Jessica Koth, public relations manager at the National Funeral Directors Association. “Therefore, families may not have the same recourse with retail stores as they would with a funeral home if, for instance, a casket arrives damaged or late,” she said.