I think the analogies you make to other types of sales aren't terribly strong. Walking through a brick and mortar store without buying anything takes effectively no time from the business - they can handle many customers in parallel. By contrast, calling prospective business or test driving a car does involve at least acknowledging the seller. You might not tell them you've bought a different car, but you also don't hear the proposed price and hang up the phone without a word, which is a closer analogy to getting an offer and replying with nothing, not even a form letter.