There was a time when it was possible to make infinite money in Dungeons & Dragons, due to a bizarre loophole involving ladders. Magic items might be incredibly powerful in D&D, but a +5 flaming greatsword isn't going to help a player climb out of a pit.
The average D&D group is loaded down with conventional items that could be useful while exploring. These include things like rope, iron spikes, bags of flour, a crowbar, and a mirror. A smart D&D player knows that it's better to have something and not need it than to need something and not have it. If this means carrying a huge bag of flour for months, on the off-chance that an enemy spellcaster is hiding with D&D's invisibility spell, then so be it.
D&D groups will often carry a ladder, in case they need to climb into a pit or reach a place that is just out of reach. It's also common for D&D groups to carry a long wooden pole, as this can be used to prod traps from a safe distance. These items combined could lead to the party earning infinite money, due to an oversight in one of the older editions of Dungeons & Dragons.
D&D: Climbing The Corporate 10ft Ladder
The third edition of D&D is fondly remembered, but it had its fair share of rule exploits. One of these involved creating salt with magic and selling it for profit, but that exploit couldn't be done until the party reached level seven. There was another infinite cash exploit that could be done at any time, at least until the DM shut it down.
In the third edition Player's Handbook (page 108), the equipment table lists a 10ft ladder as costing five copper pieces, while a 10ft wooden pole costs two silver pieces. In D&D, a single silver piece is worth ten copper pieces. In order to make use of this exploit, the player needs to buy a 10ft ladder and take out the rungs, leaving two 10ft poles behind, which can be sold for four silver pieces. Rinse and repeat. This bizarre bit of pricing remained in the 3.5 edition of D&D, but it doesn't exist in fifth edition, as ladders cost a silver piece and poles cost five copper pieces.
There are lots of bizarre rules exploits in D&D and they generally last as long as the DM's patience. It's odd that the ladder/pole exploit wasn't fixed in the jump to 3.5, but it's likely that the developers didn't think it would be an issue. A DM could shut it down by claiming the cost of both items has dropped due to the market being flooded, or maybe the prices are just different in specific towns. A player who abuses these rules could perhaps expect a revenge killing from a spellcaster who specializes in ladder golems, as a warning from the DM to not mess with their Dungeons & Dragons campaign.