Image copyright Getty Images Image caption Travellers can make some money by becoming informal couriers

The next time you take an international flight, how about transporting something in your suitcase for a complete stranger?

If your answer to that question is a resounding "no way", and the very thought conjures up terrifying images of unwitting drug mules and long prison sentences, you might need to think again.

"I always take things back from my travels for family and friends," says 45-year-old French airline worker Olivier Kaba. "Now not only am I able to bring things for others, but I get rewarded financially for doing it.

"In the past two years I have made about 1,000 euros ($1,100; £860)."

Olivier is a regular user of Worldcraze, one of three similar firms that have launched in recent years to help connect people who would like to buy something from a different country, with travellers who have spare space in their suitcase and want to make a bit of money by being informal couriers.

Image copyright Ouibring Image caption There are some products that ex-pats just cannot live without

The idea is that the buyer can quickly get his or her hands on a product that may not be available to buy or import where he or she lives (country A), or that the item may simply be a lot cheaper abroad (country B).

So with transactions made via the three companies' websites and apps, travellers who are due to fly from country B to country A can purchase and transport the products for the buyers. They can then arrange to meet to hand them over.

Over the past 24 months Olivier says he has transported everything from three months' supply of French salami to the US, bags of Japanese sweets called "Tokyo banana", and 20kg of fabric samples for a woman starting her own business.

"I discover new products I have never heard of," he says.

Worldcraze was launched in 2012 by French entrepreneurs Frederic Simons and Guillaume Cayard.

Image copyright Olivier Kaba Image caption Olivier Kaba makes about 500 euros a year transporting goods via Worldcraze

On a trip to New York Frederic noticed a large price difference between Levi's jeans in France and the US, and the idea was born.

Today Worldcraze says it has 10,000 users, with Apple products being the most frequently delivered items.

From each transaction Worldcraze takes €2.50 from the buyer, and 10% of the traveller's payment, which is up to 10% of the cost of the product being transported.

Singapore-based Ouibring has a similar business model.

Founded in 2016 by developers Joel Gordon and Andrew Crosio, they say that one Ouibring delivery is now made every day on average.

Goods delivered so far include artisan coffee from Japan to Hungary, a baby carrier from Thailand to the US, a candle carried from India, and a room spray from Singapore to the Czech Republic.

Image copyright Ouibring Image caption Joel Gordon says Ouibring flags any inappropriate requests

"For shoppers this is a way of getting previously unavailable products, full stop," says Joel.

"For bringers [the travellers who deliver the items] it's about making some money, and meeting interesting people who appreciate the effort, and can share tips for exploring the place you're visiting, or the next step on your journey."

To remove the risk of illegal or counterfeit products being transported both Ouibring and Worldcraze only allow users to buy and collect new products from legitimate shops.

Worldcraze's chief marketing officer Constance Claviez Homberg says: "Our users can't buy illegal products because they are buying products directly in shops.

"That way it is just impossible to carry illegal stuff, or counterfeit products. [And] travellers have to upload the product's bill on our platform to prove that the product is congruent."

Image copyright Worldcraze Image caption Worldcraze helped one man buy a hockey stick from overseas

The company also advises users to check on whether the item in question is legal in the destination country, and has staff that check out requests made on its website and app every day.

Ouibring's Joel Gordon says that it also has a "moderation system" which "flags requests that may be inappropriate, and we remove requests if required".

He says that the company also advises users that if they are unsure about anything they should get in touch via its secure contact form "and we'll get back to you asap".

"We are happy to provide advice for travellers for specific questions," says Joel. "At the end of the day, it is the individual traveller's responsibility to ensure they comply with the relevant laws of the country they are travelling to."

Mumbai-based Beck Friends, another firm that enables travellers to transport goods for other people, doesn't limit people to purchasing new items.

Instead a traveller recently transported a much-loved teddy bear from Chicago to Mumbai after its owner, a four-year-old girl called Heer, left it behind.

Image copyright Beck Friends Image caption Beck Friends helped reunite Heer and her bear Teddy

To remove any security concerns, the buyer and carrier have to be first connected on social media, such as on Facebook, LinkedIn or Google+. Users must also upload two valid forms of identification, such as a passport and driving licence.

Beck co-founder Deep Malhotra says: "Security is the prime concern, and we are building a robust platform to address this."

Where things get more complicated is the issue of export and import tariffs, which vary greatly from country to country. All three companies say they advise users on this, and it is the buyer who ultimately has to pay any charges.

If any traveller is unsure of something, or gets into any difficulties, all three companies say they have support staff available around the clock to help, be it via telephone, live web chat or email.

Ouibring's Joel Gordon says that he doesn't think security or customs worries will hold back the growth of his company.

"Our vision is to become another part of daily international life, like Airbnb, with people all around the world helping to make transport, logistics and travel work together better."