system
Given the following post, respond as if you're commenting on Reddit:
human
[Harry Potter] How can the Weasleys be poor? For that matter how can any witch/wizard be poor?

Even if you can't just create food or "money", with magic you could be a tycoon easily:

Import/Export using something similar to the vanishing cabinet, real estate (for a magic community), digital currency (not everyone can got to gringotts when they need to put something in savings), efficient factory designs (hell you don't even need the factory!). 

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Your house is crooked? Fix it! Need more room? Expand it! Need food? Charm your garden!

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The argument that magic is supposed to be protected from muggles shouldn't come into play here because there are plenty of opportunities for A. wizard specific markets or B. hidden magic (i.e the magic used to surveil muggles (book 6) or the magic used to repel muggles (book 4). I'm not saying you need to give magic items to muggles, but instead build a business that uses magic to create profit. 

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Even if most of society is so isolated from muggles and it doesn't cross their minds, there are hundreds of muggle-born witches/wizards that go to hogwarts.
gpt
The Weasley family is only poor by the standards of their social peers. Much like the old English landed gentry, anyone who actually *needed* to work would be considered poor by the metrics they apply, regardless of how much land they hold, how many children they send to an elite boarding school, or anything else they have going on. 

In terms of actual resources, Mr. Weasley is held back a bit by his choice of job; it's a reasonably secure position, but there isn't a lot of money or room for advancement in monitoring Muggles. Contrast that with the twins, who set out into the business world as independents with novel products and manage to do very well for themselves in a relatively short time. Other wizards could set out in similar fashion and succeed or fail much like muggle entrepreneurs often do.