SINCE it is so easy to find a car or bike available for “sharing” on Shanghai’s streets, I often wonder about doing some soul-searching about this new trend.

The emerging sharing economy over the past one or two years has managed to survive sabotage, hoarding, losses and all kinds of accidental damage. It has also stirred debate about human nature — and not all of it is optimistic.

“I don’t think we have quite arrived at the level of civility that enables sharing,” said my friend Vincent, who takes a hardened, hopeless stance against my optimism.

He comes from Chongqing, a pilot city for car sharing in southwestern China, and said it feels all too familiar seeing the colorful two-seater cars that zoom around his hometown suddenly appearing in Shanghai for hourly rental. To him, it feels like the calm before the storm.

I remember the headlines about how some hot-tempered Chongqing local just abandoned a car-for-share at a parking lot’s exit to protest a dispute over parking fees. Vincent has his own more personal anecdotes about the perils of car-sharing. He said he once rented a car with a takeaway Chongqing hotpot spilled all over the seat by the previous driver. The smell and the stains were hard to wash away.

“I have definitely seen worse,” I said, trying to hold back a laugh.

In a photo widely circulated online, a thin needle is shown sticking up from the seat of a bike-for-share. The thought of what could possibly motivate someone to do that made me cringe. There have also been photos online about the scan codes to unlock shared vehicles being smeared beyond recognition, bikes-for-share piled up like garbage or even dismembered for resale with just a stump left.

It’s not hard to guess who might be behind all this vandalism. Careless users, childish pranksters, street thugs, calculating thieves. The list of possible culprits sows deep seeds of disappointment in the selfishness of humans, and it certainly doesn’t help the image of a sharing economy.

Last week, a local bike-for-share company in Fujian Province went broke after nearly 80 percent of its bikes went missing 19 days after its service was launched.

The drawbacks aren’t crushing the high hopes of companies that view the sharing economy as a beneficial investment. Across the country, many companies in the business are expanding their footprints.

In Shanghai alone, there are two major operators offering car-share and about 10 bike-for-share services. All use vehicles with distinctive styling or paint to lift their profiles. Whenever I see these colorful wheels roll by, I start to worry that industry latecomers may be at loss to come up with even more innovative ideas to stamp their signatures on the streets.

“How many of those companies do you think will still be operating next year?” I once asked my friend Andrew, who works in the venture capital industry — a prime investor in the sharing business.

I find it ironic that an industry that prides itself on making money by exploiting human greed can invest in a business model that relies on human honesty and trust.

“I don’t think it’s about overcoming our selfishness,” Andrew told me. “When most people come to find themselves beneficiaries of the sharing economy by saving money and enjoying convenience, they play by the rules and even take exception toward those who violate them. It has nothing to do with altruism. It just becomes a new life order you don’t want to be disrupted.”

His words evoked memories of Scandinavia, where I was once an exchange student. It’s a peaceful part of the world where bike-sharing was warmly embraced by the public early on. Upon arrival, I was surprised to find that locals would leave their private bikes unlocked by the roadside. Several other Chinese exchange students and I hatched a plan to pinch one of the bikes and then return it a few days later, just to show the owner the risk of unguarded trust. But later on, the mere mention of this idea embarrassed us because it would ruin something beautiful and precious that we found no longer distant, and grew attached to.

In China, it is not easy to bring every person who violates sharing rules to heel and make them pay for their actions.

Some sharing company encourages users to be “knights on wheels” by reporting the misbehavior of others in exchange for credit points that can lead to discounts. Law enforcement and the judicial system are also taking action by identifying rule breakers and fining them or taking them into custody.

But there are times we involuntarily betray the trust that we can be responsible members of the society because we are so lack of certain practice that the ultimate boundaries have yet to be firmly established.

Because of the explosive growth of bikes-for-share businesses, some downtown areas of Shanghai have reached their capacity for parking cycles. A district recently seized 4,000 bikes-for-share, stirring a controversy over how much the sharing economy should be allowed to eat up public resources.

The spirit of sharing can even take on a life of its own. A code manual has been compiled and circulated on WeChat, showing how people can get free rides at a bike-for-share service that uses combination locks. For every half an hour, one can save 1 yuan at most.

“Is that really worth all the trouble?” I sneaked into one of those WeChat groups, out of curiosity. I wondered whether these people are really so poor that they are willing to cede their sense of common decency.

My question was answered by another question. “Do you really think those sharing companies care about making money from our payments?” The cynics seemed to think that the safety deposits charged in advance of hiring a shared bike are being used clandestinely to invest in other businesses rather than being held in deposit for refund.

I hate to tell them this, but the “grey zone” of safety deposits that inspires their conspiracy theory is now coming under supervision by banks.

Sharing companies don’t stand to make a lot of money for the time being, given their low-pricing strategy, low-quality maintenance and aggressive deployment. Their profit prospects will no doubt clarify doubts about the sharing business being just another example of market-invented hype.

No company wants to run a business like a charity, even if its credentials are eco-friendly. It is against their self-interested nature.

If only a hidden agenda can satisfy some people’s imaginations about businessmen being shrewd and dishonest, I do have some theories. Think about the maps that can be completed with GPS-equipped bikes for narrow back lanes and think of the expandable scope for desirable new home locations as more shared bikes and cars are available from Metro stations. Surely these offshoots will generate more business opportunities. Just as priceless are the lessons they teach us about what kind of people we can choose to be.

Mia is an independent market observer.