I would not be surprised if they bribe the employees.

That would be difficult to pull off without collusion with an insider doing an end run around the support platform. The support platform is heavily locked down (to a degree I've never seen with other retailers) and surveilled.

But it sounds like it would be trivial to look the other way on these investigations, as evident by their repeated lack of action.

Most likely though someone at Amazon doesn't want to hurt their metrics for sales/relevance.

Is that so unlikely? People commit treason for $100k. Here we’re talking about much, much more at stake.

and much less in the way od punishment

Not necessary. Amazon doesn't need to bribe anyone because no one bothers to hold them accountable.