Hey there! To clarify the royalties, the section that is being referred to is" The first $3,000.00 in gross revenue for each Product per calendar quarter".](Game-Engine-Technologie von Unreal - Unreal Engine) So you would making a decent amount of money per quarter to hit that threshold.
To answer you question about how Epic locates developers that try to go around Epic’s agreement with them, we intentional do not reveal what our techniques are so people will now be temped to bypass them. Anyone that is found to be doing this intentionally will usually face legal repercussions.