Perhaps she'd be willing to pay $100 for a widget if there were no other option, but would nonetheless prefer to pay less if that can be arranged.

Transaction and information costs are a huge problem. People spend a lot of time paying them in actual life — for instance, driving to work or to the store; standing in lines; searching for bargains; clipping coupons; and so on.

Alice is willing to incur an email round-trip time to distinguish a world where $100 widgets are the only offer from a world in which a $90 widget is also available. She considers that the delay of one round-trip of haggling is worth $10 times the probability of a lower offer existing.

(Other factors obtain, too, like minimizing regret ­— if she bought a widget for $100 and then immediately saw Bob sell one to Faye for $90, she'd feel like $10 worth of fool.)