You don't.
Everything about this article feels like it was written by someone who has no idea what they're talking about. At all. Remotely.
The sources linked in the article have
nothing to do whatsoever with the notion this article puts forth about "Buying and re-selling V-Bucks"
One of them is about fake "Free V-Bucks" sites that are Phising operations, another is about shovelware apps on Google-Play/App Store which are used by credit-card thieves to siphon money (doesn't even mention Fortnite at all in the article), and one of them is basically the same article which this one basically copied verbatim - Which also has no fucking idea what it's talking about.
Here's a quote from the article's source-article:
There is so much shit wrong in this quote. You can't "Transfer" V-Bucks or any items at all in Fortnite. There is no trading or anything whatsoever. And since when did having a lot of V-Bucks become a felony?
Oh and by the way, the party that carried out this "investigation" is The Independent - A fucking
infamous terrible clickbait-bullshit site.
CONCLUSION: This entire article is bullshit clickbait with a half-assed investigation done by a bunch of old men who have no fucking clue what they're talking about.