Applying for a job as a policeman in Bali is not as simple as filling in a form. You may need to pay $50,000 or more just to be hired.

The exact amount varies by how much you'll be able to extract during your career in bribes and kickbacks, so not surprisingly, buying a job in a "wet" area – such as traffic or vice, which is likely to yield the biggest money – costs the most.

Bali's tourist trade makes it the most lucrative Indonesian province for police by far, so the most attractive for police work.

In April, a Dutch tourist exposed how lucrative the traffic division could be when he secretly filmed himself being shaken down for not wearing a helmet, then posted it on Youtube.

So when seven Australians were unwise enough to hire a buck's night stripper at a bar in Kuta earlier this year, they were creating an opportunity.

Police were probably tipped off by the bar or security guards. It's quite common for senior police to be silent partners in bar ownership in Kuta. They have a hand in the drug and sex trades. They associate with the street gangs and bouncers who act as enforcers and run protection rackets.

Money earned by police in these situations flows up and down the ranks, buying discipline from lower-downs and protection from higher-ups, according to Murdoch University academic Jacqui Baker, who has made a study of the black economy in the Indonesian police force.

If the bar owner did not get a cut of the $25,000 proceeds of the buck's night sting, then the superiors of the officers involved almost certainly did.

To corrupt police, foreigners are "fantastic, low risk targets".

"They're disconnected from any Indonesian network, so they have no patron or political power of their own. And they throw around cash. They're like an ATM, you just kick them and they spit out money."

Baker advises tourists to stay below the radar: wear the helmet, keep your wits about you, don't antagonise anyone.

If you're caught out, the best advice appears to be to do what these seven Australians did: pay up fast and leave the country.

What's most surprising about this story, though, is that the police involved have actually been caught.

Time will tell if they actually receive punishment.