On one hand, if they don't have to charge 7%, they're not that successful as to sell $1m a year.
On the other hand, customers have to pay the 7% imputed into the cost anyway, since they can't recover GST on their own expenses from the government unlike a GST registered trader.
I support display of net prices because: 1. it makes it easier to gauge the price you're paying 2. it makes it easier to split bills 3. the 10% service charge collected by an eatery doesn't necessarily have to be paid to the staff; the owner has discretion whether to do so or not in his agreement or collective agreement with the staff.