Eli Cohen infiltrated the Syrian establishment by pretending to operate a successful business (as Kamel Thabeet). Surely, even a cursory inspection of his ‘company’ would show it didn’t exist. How did this remain undetected?

The problem for the Syrian authorities to verify his background was that Eli Cohen spent in fact some time in Argentina, specifically for the purpose of building up his cover story. He ran a business in Argentina, made a lot of rich friends in high society there, and even in his native Israel he had held real jobs as a businessman.

Eli Cohen therefore learned to come across as a genuine business man. On top of that, we are speaking about the 1960's. It wasn't as easy back then as it is today to collect records and information about people, and certainly not if its abroad. Eli Cohen also exploited the human tendency that swindlers and fraudsters exploit to this day: laziness. If you appear legit, people are willing to believe anything you say and not go through the bureaucracy to check it.

On top of that, they would have to have a reason to verify his credentials. Cohen first established friendly relations with very influential political Syrian figures in Buenos Aires, from the Syrian embassy. By the time they invited Cohen to come to Damascus there to set up business, no one in the top echelons suspected anything wrong. Cohen had spent several years training to appear like a genuine Arab, learning all the linguistic subtleties and cultural traits.

His regular trips to Israel to meet with his handlers did however eventually generate suspicion among Syrian intelligence. This in combination with the fact that Cohen leaked certain detailed information to Israel that few other people couldve known about. The Soviet technicians eventually warned the Syrians that Eli Cohen was transmitting messages to Israel and busted into his apartment to catch him in the act.

So in short, Eli Cohen was an expert in convincing people of his role, they had limited means to verify his story, and for years they had no reason or suspicion to do so. When he did eventually attract unwanted attention, he was relatively easily caught.