Well worth a read. See link below.
My take is that the refund should have been for the full amount, as the discount only applied to the first $150
Have always been refunded the full amount not a discount amount, even when the $ become less than a qualifying spend.
http://www.news.com.au/finance/business/retail/woolworths-he…
The maths in that article is clearly wrong.
However the general principle of refunding by % discount you paid for is right I think. You shouldn't be refunded the full amount because you didn't pay the full amount.
The voucher is not $10 off for the first $150 spent, nor is it $10 off per $150 spent. It is $10 off your entire order, provided you meet the conditions (that you spend at least $150). So he received $10 off his order of $350, equating to a 2.85% discount.
It shouldn't matter what the conditions are (i.e. regardless of whether it was $10 off your order if you shop on a Wednesday, $10 off your order if you spend at least $30 from the meat department, or $10 off your order if you pay with a wish gift card) for obtaining the discount.
Therefore I personally think the fair thing would have been to refund him $7 * 97.15% = $6.80 OR $7.00 store credit, since he paid $6.80 to purchase $7.00 retail value of goods.