Shooting yourself in the foot.

I am a supplier of a service for which you can pay in one of two ways - A and B. I wish to encourage you to pay by method A. I can do one of two things - I can say "the cost of my service is £100, but if you pay by method A I will give you a discount of 3%", or I can say "the cost of my service is £97 but if you don't pay by method A I will charge you an extra £3". The practical effect is exactly the same - if you pay by method A you will pay £97, if you pay by method B you will pay £100. But for a method B payer the perception will be quite different - in the second instance you will feel you are being penalised. So why would BT, who want to encourage people to pay their phone bills by direct debit, choose to be seen to penalise those who don't rather than reward those who do? Like I say, it's all about perception.