I think the point is that even if it's only a one time study, a default strategy of preferring free to paid can be rational since we participate in a huge numbe

I think the point is that even if it's only a one time study, a default strategy of preferring free to paid can be rational since we participate in a huge number of transactions in daily life. You are viewing this as an irrational sacrifice of quality for $0.10, but it's really a question of longterm strategy, even if the calculation is done on a subconscious level.