Two diners sharing a bowl of soup, people ordering pots of hot water, three mothers with prams taking up a table for six and the demanding diner who doesn't tip. It may be the hospitality industry but it turns into the hostility industry when a waiter waves a finger and the customer waves their weapon of mass destruction – their mobile phone - and seeks revenge with vitriol on Urbanspoon. And given anyone with tastebuds and an internet connection is a "food blogger", these self-appointed zeitgeist Nazis resort to blackmail.

At Brunswick West cafe John Gorilla, a woman ordered a $1 babycino and hogged a table for four hours to use the free Wi-Fi. After the cafe debated the issue on Facebook, a negative review appeared on Urbanspoon: "Don't advertise free internet and then make me feel like I'm breaking the law."

Raymond Capaldi, owner of Hare & Grace, was staggered when two customers shared a latte – a latte! – after a shared entree and main course. "They tell you they're not hungry then eat six loaves of bread," he said. His annual bread bill is $60,000 for artisan loaves from Shannon Bennett's Burnham Bakery and a shared $3.50 latte won't cover the cost.

Mr Capaldi has experienced bloggers "blackmailing" him because they believe the restaurant owed them. "When they buy a Gucci bag, they don't think anything of the cost. When they're buying really good chicken or artisan pork, because they can't wear it they can't see the real cost."

Customers won't be able to sit on a salad and admire the linen tablecloth in the opulent Mural Room at Grossi Florentino because it switched to a fixed-priced menu – $95 for 2 courses or $120 for three – "to give people a package so they know what to expect".

A la carte is slowing disappearing from fine dining, and set menus are de rigueur at Vue de Monde, Attica and Brae. And at Prix Fixe, customers have to buy a ticket and pre-pay $49 for lunch and $79 for dinner.

To ensure viability and longevity, restaurants are pulling the linen tablecloth from under the scenesters. Trendy Collingwood 40-seater Saint Crispin has a minimum spend – two courses for $50 or three for $60 – and two sittings. With an  eye on economics and profit of  2 to 3 per cent, chef Joe Grbac said: "We were very wary of overheads and were concerned that with what we were trying to offer – a  neighbourhood restaurant – people would order a side for their main course and sit there for three hours."

If customers only want one course, they are directed to the bar.

Leader of the casual and affordable dining craze, Chris Lucas from Chin Chin and Kong, supports set prices because they ensure restaurants can deliver a full experience.  "Set-prices guarantee a minimum amount of revenue to cover the basic costs of running a high-end restaurant."

Becco manager Simon Hartley takes a different view to young couples who don't have a big budget. "You have to treat them like kings because one day they will have money."

One way to beat the scenesters is to copy London's Ziferblat, a "social network" that charges people five pence a minute. There's no such thing as free Wi-Fi.