Prompt and skill marketplaces have a genuine appeal. One-time purchase, no subscription, a file that's yours to keep. Compared to a recurring AI subscription, it feels like buying a tool instead of renting one.
Here's the part that doesn't show up in the pitch: you're buying instructions, not a result. And you usually can't tell how good those instructions are until after you've paid, set everything up, and run it yourself.
What you're actually buying
A listing on a prompt or skill marketplace is almost always a text file. Sometimes it's a prompt meant to be pasted into a chat window. Sometimes it's a more structured file meant to be installed into a coding tool. Either way, the thing you own after checkout is instructions someone else wrote, not a finished result they've already produced.
That distinction matters because instructions only work as well as your ability to follow them correctly, feed them the right input, and, in some cases, connect them to a separate service they depend on. A skill that removes backgrounds from images, for example, might actually be a wrapper around a different company's API, which means a second account and a second bill before you've processed a single image. None of that is disclosed up front in a way that's easy to notice.
The part you can't check before paying
With almost anything else you buy, you can look at it, read reviews, sometimes try a demo. With a prompt or skill file, the listing shows you a description of what it does, not the thing itself. You find out whether it actually works only after you've paid, installed it correctly, and run it against your own real situation, which is exactly the point where a "does not do what I expected" problem becomes your problem, not the seller's.
Some marketplaces have started embedding a unique buyer identifier into each file you download, mainly to trace unauthorized sharing. Reasonable on its own, but it's a small signal of the broader shape of this model: you're licensed to use a static thing, not handed a result.
What to actually look for instead
The fix isn't avoiding marketplaces entirely. It's noticing the difference between two very different offers that look similar at a glance:
A file you have to set up before you know if it works, versus a result you can see before you commit to anything.
If you can run something and look at exactly what it produces before paying or installing anything, you're evaluating the actual output. If all you can see is a description and a price, you're evaluating someone's writing about the output, which is a different thing entirely.