Indonesia's motorcycle taxi candidates test.

So stiff is competition between Indonesia's motorcycle taxis app companies that new entrants are going to extreme lengths to stand out.

Aris Wahyudi, the founder of the newest motorcycle-sharing company, reckons he has found a unique way to win business: not-so-smelly drivers.

"We took the decision to do an odor test for our customers' satisfaction," Wahyudi said, speaking in a sweltering basement car park, where prospective drivers are lining up to have their armpits sniffed as part of a selection test.

Dozens of companies have set up in Indonesia in the past year or so, seeking to emulate the success of Go-Jek, the first local firm to use smart phones to tap into the country's millions of traditional motorcycle taxis, known locally as ojeks.

There are now nearly 40 such firms operating in Indonesia, including Malaysia's GrabBike, and local firms Ojeks Syari, which advertises the Islamic credentials of its jilbab-wearing, women-only drivers, and Limobike, which offer a deluxe service with Vespa-style scooters.

Endang Ahmad, 37, takes his job as a professional armpit-sniffer very seriously.

"I have already found many types of body odor smell," he says, clutching a clipboard which he uses to score candidates as they stand, arms outstretched, in front of a fan meant to simulate the headwind of a motorcycle ride.

"The ones who have sweat smell and armpit smell mixed we don't give a pass."

How to respond to the rapid expansion of ride-hailing services in Indonesia, a mostly tropical, sticky country of some 250 million people where public transport is patchy, has caused friction within the government.

Last month, President Joko Widodo overturned a ban on such services only hours after his transport minister imposed it, amid a popular outcry on social media.

Wahyudi, a former electronic engineer who took money from friends, family and investors to set up UberJek, which has no connection to global car-sharing service Uber, says his company is the only one to conduct such stringent smell checks.

When the company launches in a month or two with some 3,000 drivers, customers will be able to use the app to rate drivers based on their smell. Drivers who accumulate too many negative reviews will get a warning and could be suspended if they fail to scrub up.

Muhammad Ali, 44, wants to supplement the salary he earns working in a bank by driving a motorcycle taxi in the evenings. He has come prepared for the odor test.

"I have brought Rexona (deodorant) because, according to my wife, I have smelly body odor," he said. "But I am really optimistic I can pass all the tests today."