I imagine that, in these experiments where the subject is offered a choice, one must take care that the experimenter does not subconsciously signal the 'smart'

I imagine that, in these experiments where the subject is offered a choice, one must take care that the experimenter does not subconsciously signal the 'smart' option, such as by the counter-party in a bartering exchange being unaware of the problem that the subject is being tested with, and by avoiding having decoy objects that are more similar to each other than they are to the tool.