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This has been a problem for a long time, honestly. I used to be a staff member, so it wasn't that much of a problem, but it was still stressful....
What I do is start with a cobblestone generator, don't forget to enable it at /is settings and upgrade it at /is upgrades. Once you have enough...
Maybe involve that the players aren't allowed to say it in chat ;) Maybe add: Scamming is at your own risk!