In the last of a series from the Thai-Burma border, the BBC's Kate McGeown looks at trade between the two nations, including the thriving black market.
The river Moei forms a natural divide between Thailand and Burma - and separates the Thai border town of Mae Sot from its Burmese counterpart, Myawadi.
If you go down to the river during the day, it looks a quiet, peaceful place.
A few people wander across the large Friendship Bridge connecting the two countries, but most are asleep at home, or idly chatting with friends.
At night, though, it is a different story. Suddenly, all the people on the riverbank spring into action, rowing or even swimming across the water, laden with commodities to sell on the other side.
This nocturnal trade is easy enough to explain: While Thailand has relatively few import and export restrictions, the Burmese government has banned the import of many basic commodities, to ensure it retains tight control over the movement of goods.
It also makes life difficult for exporters - who find themselves saddled with high taxes and lengthy delays while their applications are being processed.
The result is a thriving black market. Merchants cross over the Friendship Bridge during the day, agree to buy certain goods, then come back empty-handed.
As dusk falls, boats, rafts and even old tractor tyres start appearing, ready to haul the relevant items over the river to fulfil the merchants' orders - avoiding the officialdom on the bridge.
Bribery system
This cross-border trade works on a well-organised system of bribery.
One man, who spends every evening moving furniture from Burma to Thailand, said he has to pay bribes on the Burmese side, the Thai side, and even to cross a small island in between.
"I get paid 250 baht ($7) for taking a pile of chairs over - I have to pay 100 baht to the Burmese, 50 baht to the Thais and 30 baht on the island. The rest is my fee," he said.
Suchart Treeratvattana, the former chairman of the Chamber of Commerce in Tak province, which includes Mae Sot, admitted he knew that this nocturnal trade was happening.
"Obviously it's a problem for the other end, but it doesn't concern Thailand," he said. "After all, the Burmese people need these commodities."
Mr Suchart was less ready to admit to other types of cross-border trade, though.
Gem trader
He denied any knowledge that sex trafficking took place, although Mae Sot is thought to be one of the main routes through which women are being trafficked into Thailand.
He also said that since the drugs crackdown under former Prime Minister Thaksin Shinawatra in 2003, narcotics are no longer being brought over the border from Burma to Thailand.
But according to the United Nations Office on Drugs and Crime (UNODC), there has actually been a recent increase in the amount of amphetamine-type stimulants (such as the popular drug Ya Ba) crossing the border, despite a reduction in the smuggling of opium and heroin.
Jade trading
Another, more obvious, type of cross-border trade is in gemstones.
The Tak Chamber of Commerce does not keep data on how many precious stones are brought into the area from Burma; Mr Suchart said that official figures were so small as to be insignificant.
But you only need to walk down one of the main streets in Mae Sot to see that while legal gem trading may be practically non-existent, the illegal sale of Burmese gemstones is flourishing.
A merchant in one of the town's many jade markets estimated that Mae Sot had about 1,000 gem traders.
She explained that she had little choice but to come over the border and sell her wares in Thailand.
It is very easy to find Burmese gem traders in Mae Sot
Her family owns a small mine in the northern Burmese region of Mogok - where most of the country's sapphires, rubies and jade come from.
She said that if she tried to sell the stones in Burma, the authorities would demand the best ones for themselves, so she could not make a living.
Instead, she hires people to bring them across to Mae Sot.
"Sometimes the carriers hide the gems inside their bodies - I don't ask how they do it," she said.
"Our carriers have to be people we know well, as we have to really trust them. Twice last year, I used a carrier who ran off with my jewels."
While the gem traders in Mae Sot - both Thai and Burmese - are looking to gain from this illicit trade, the real winners are the foreign buyers.
In one shop I met a Sri Lankan dealer who was buying a blue star sapphire for 400,000 baht ($11,500). He confessed he could easily double his money, selling the stone on the international market.
Increasingly alone
The Burmese are such a huge presence in Mae Sot that you can never forget the country's proximity to this industrial Thai town.
In some ways - notably cheap goods and labour - Thailand definitely benefits from having such a poor nation on its doorstep.
But as the poverty gap rises, and Burma's problems get progressively worse, the positives are being increasingly outweighed by the negatives.
It is not just Thailand that is getting fed up with Burma. The regional grouping Asean (Association of South East Asian Nations) and the international community are gradually losing their patience as well.
They are frustrated by the government's continued refusal to progress towards democracy, and angry at the poverty, human rights abuses and high levels of black market trading, such as that seen openly in Mae Sot.
Perhaps it is apt that so few people are going over the Friendship Bridge.
Right now, Burma does not seem to have many friends left.
Read the previous three articles of Kate McGeown..
Saving lives on the Burmese border
The fighting spirit of Burma's Karen
Life on the Burma-Thai border