The mandated fee-cap introduced a few years ago has (or rather should have) curbed the view that overdraft fees are a cost centre. Banks are extremely proactive now, as soon as there is a hint you'll go in the red they'll ping you in a bunch of ways and remind you of what you can and cannot do; so I wouldn't exclude that some (or all) might now refuse to complete purchases when it would push you too deep into unarranged territory, because they cannot charge you more than a fixed amount, so it would become basically a free loan.