What buyers perceive to be their best interest at the time they buy may certainly seem irrational to others.
Of course, in hindsight, with all the information in hand, buyers' actions can be described as irrational. But at the time of the transaction, only irresponsible, reckless, intoxicated or mentally impaired buyers do not act (buy) in what they perceive to be their best interest. Even high-risk purchases, speculative investments for instance, are made after the buyer decides the risk is worthwhile.