Can variations and evaluations be manipulated?
Since Let's Check is open for all engines it is possible that old, bad or manipulated engines can be used. Destructive content is always possible whenever people can share content in any form of online community.
The hardware power and the processing time of variations play a role, so it will be difficult to falsify an analysis even if an engine has reported having made the deepest analysis.
In the Let's Check window we also see how often a variation has been verified by other users. The system cleans itself, and so unverified variations and the obsolete evaluations of older engines will disappear with time.