However, on the long "pay-as-you-go" routes, such as the one from Eritrea to Israel or from Somalia to South Africa, migrants generally only know the smugglers who take them on the first leg of their journey.
Thereafter, they may travel alone for part of the way or be passed from one smuggler to another through what Horwood describes as "informal chains" or "loose alliances" that differ from the more organized networks typical of human trafficking.
Obstacles to prosecution
The extent to which abuse by smugglers occurs, even on the most notoriously dangerous routes, is unclear. "Most stories you hear are the stories of the people who had a bad experience with a smuggler.
You don't tend to hear the stories of the people who didn't experience abuse," said Sanchez, who argued that the majority of migrants do not experience abuse at the hands of smugglers.
Those migrants who do experience abuse rarely report it, particularly if they have reached their destination and are trying to steer clear of the authorities. The lack of formal complaints by migrants has added to the difficulties of prosecuting smugglers, who can be difficult even to identify.
"Unlike trafficking, smuggling isn't done by professionals, it's done by people who have other jobs. These aren't arch-criminals, but people who are making money on the side," said Khalid Koser, deputy director of the Geneva Centre for Security Policy, who has done extensive research on migrant smuggling.
"There's no profile for a smuggler," agreed Sanchez. "The smugglers I interviewed in Arizona [near the US border with Mexico] were teenagers who guided people through the desert ... you have a single mother of three who was housing people overnight and... grandmothers feeding people." Migrants may also assist by cooking at a safe house, steering a boat or driving a vehicle in return for a lower fee. This sometimes results in their arrest for smuggling.
"The determination of who is a smuggler is quite problematic. We think about smuggling as becoming more organized and structured, but what we're actually seeing is how the risk is being transferred onto the migrants and refugees," said Sanchez. "Most of the people who are prosecuted for smuggling are migrants themselves."
Even countries that are signatories to the Smuggling Protocol often have no specific legislation to target people-smuggling. Samantha Mundeta, a regional legal adviser with UNODC's Southern Africa office, noted that most countries in her region rely on immigration laws that "tend not to get to the bottom of the crime [smuggling] and the people who perpetuate it", and which are more often used to criminalize migrants.
"There's no attempt to go after the smugglers, it's all about irregular entry by the migrants," agreed Getachew of IOM, who says the lack of capacity and resources in local law enforcement authorities has also hampered efforts to investigate smuggling.
UNODC has set up a voluntary reporting system in Asia that allows countries in the region to collect and share data on smuggling trends and networks. In eastern and southern Africa there is no such system, and "weak coordination regionally on these issues", said Mundeta.
The role of corruption in facilitating almost every stage of a smuggling operation presents another major obstacle. In a paper published recently by UNODC, the authors note that "Migrant smuggling could not occur on the large scale that it so often does without collusion between corrupt officials and criminals."
Smugglers are often able to bribe their way out of trouble, and the combination of corruption and light penalties for the small number of smugglers who are prosecuted has made it "a very attractive activity" for criminals, commented Horwood.
Several researchers IRIN spoke to suggested that the most effective deterrent to smuggling may be fewer border controls, not more. "Countries tend to focus on border security, and that doesn't seem to work," said Koser. "The unintended consequence of more restrictive immigration policy is more illegal migration."
In the West Africa region, where a protocol on freedom of movement allows people living in member states to travel within the region without visas, there is little demand for smugglers. "Smuggling can't operate without restrictions," said Horwood.
"We need to look at visas and passports, we don't need to look at any more criminalization or deterrents," said Sanchez. "We need to look at mechanisms that are going to facilitate mobility."
However, the political sensitivities that inform debates about irregular migration around the world make it unlikely that such mechanisms will be introduced in the near future.
As long as public sentiment remains anti-immigration, governments will continue to make it more difficult for migrants to enter their countries legally, perpetuating the demand for smugglers.
[This report does not necessarily reflect the views of the United Nations.]