But such unsolicited pestering is far from a rare occurrence in the city. Shanghai-based blogger Adam Minter wrote this week about a similar experience in a supposedly respectable electronics store in the city's main shopping district. He was stopped by a spiv trying to fence apparently stolen iPhones - within plain sight of the shop's sales staff.

Just a month after the end of the World Expo in Shanghai, the weevils are crawling out of the cracks again.

Not that they were ever really hiding.

On the face of it, Shanghai is a prosperous, aspirational metropolis. Scratch just below the surface and you will reveal a seething mass of sleaze and corruption.

All major cities of the world have their difficulties with organised crime. Hong Kong has its problems with triad societies, for sure. But other than walking past the short stretch of girlie bars on Lockhart Road or straying onto the darker parts of Portland Street, it is unusual to come face to face with evidence of their existence.

In Shanghai, the underworld's presence is considerably more blatant. The gangster element is all-pervasive, to a degree that makes it hard to imagine the police are unaware of their activities, if not complicit.

This ranges from the relatively harmless pirated movies - it is hard to call it 'copyright theft' when there is no official import of most foreign films - to the strong-arm thugs who enforce the overcharging scams that the city's not-quite-a-brothel bars perform on unsuspecting foreign businessmen.

In the run-up to the six-month-long mega event that was the expo, the city's authorities made a song and dance about cleaning up the less law-abiding elements of society, with particular emphasis on the sex trade and unlicensed taxis.

But a song-and-dance performance is exactly what it was. There were a few high-profile raids on saunas, but most continued to operate. The strips of dodgy drinking wells on two of the most notorious streets were unceremoniously shut without notice. But the seedy establishments didn't go away, though. They merely moved underground - literally. Shanghai now has a subterranean shopping mall dedicated to nefarious nocturnal entertainment.

Even in the respectable bar districts, shady-looking characters wander the streets offering marijuana to passers-by. During the expo they simply whispered a little quieter and kept to the shadows a little more. Discretion is the key.

Likewise, the shops selling bootleg DVDs closed down for a few days. They reopened after a dividing wall had been installed separating the stores into two rooms: a handful of legitimate discs on the outside; a collection of copies concealed behind an unmarked door.

Before long those doors were left open, turning the pretence into a farce that continued until last month.

Now that the expo is over, the city's underbelly has reared up with glee. Even before last month's fire disaster - which sparked widespread suspicion about official corruption and incompetence that may have contributed to the 58 deaths - Shanghai locals were talking in hushed tones about a sudden surge in lawlessness.

There has been a spate of violent attacks in public, including a youth wildly swinging an iron bar at domestic tourists in the street, apparently at random. A Japanese-Canadian man was stabbed to death while sitting outside a well-to-do restaurant inside a shopping mall - an event that was swiftly purged from Shanghai's news websites.

Most of these look to be isolated incidents, but they have the combined effect of prompting many to stop and wonder just how safe they are in this city. And there is little public confidence in the Shanghai police to clean up the situation. They are broadly caricatured as being lazy and on the take.

Pub owners, for example, say in private that they are 'requested' to subscribe to several magazines the police force allegedly produces. Official receipts are provided so it all appears open and above board. The magazines might never arrive, but the payments continue nonetheless. Nobody need specify what would happen if they stopped.

It is hard to imagine the pimps brazenly touting their 'ladies' in convenience stores or flogging dodgy phones in electronics shops haven't come to some kind of similar arrangement.

This is a city where everyone is on the make. For some residents, that's part of its charm - a bit like living in the old Wild West.

Until you end up on the receiving end, that is.