I think you did enough due diligence by putting the random part first, but I suppose one way to stop someone from putting in a real BIP39 mnemonic would be to use a completely different set of words than those allowed in BIP39.
- formal or material (do you want the bad thing to happen and that's why you're buying from Amazon?)
- immediate or mediate (are you supplying a critical component such that without your specific instance of cooperation the evil could not occur?)
- proximate or remote (Do you work for Amazon?)
Each of these dimensions should be taken into consideration because without such analysis one can easily become scrupulous about every act that one does that may have unintended side effects. This is how you get people who say things like "there is no such thing as ethical consumption in capitalism" and other extreme statements that would otherwise force you to be a monk in a desert lest your acts accidentally create harm.