so thinks about this, you head on down to the gas station to top up the gas tank in your car, you want $20 of gas. The guy at the counter says "pay first", "no problem, here use my eftpos card to take $20". You hand off your eftpos card and notice that that only $1 is showing on the eftpos machine, the gas station guy says "Yeah, we just want to make sure that you have a valid card before we do another transaction for $20, we will do a reversal in 1-7 days".
Would anybody be willing to part with $1 on every eftpos transaction for 1-7 days?, I think not!
It wasn't too long ago that when you used your CC at certain Petrol Stations they would put a hold on your card for up to $150 which would sit there for a few days (no matter what value you ended up pumping). I remember when Pak n Save Moorhouse in Christchurch introduced self-serve fuel pumps this was standard practice and caused a lot of grief. Not the case as far as I know these days.