Money: You pay them.
Ideals: Appeal to their ideals. Say in this case, protecting the Jewish state.
Coercion: Blackmail
Ego: Make a powerless bureaucrat feel important on a historical scale.
Top three countries that spy on the US:
1) Israel
2) China
3) France
http://www.theregister.co.uk/2009/10/20/nasa_security/
Mr. International Espionage was apparently a really cheap date: $9,000 for "... information classified as both top secret and secret, on U.S. satellites, early warning systems, means of defense or retaliation against large-scale attack, communications intelligence information, and major elements of defense strategy".
http://www.huffingtonpost.com/2009/10/19/stewart-nozette-pic...
Did you read the article? It was an FBI sting - no Israeli involvement. In fact, from your HuffPo link:
>The complaint does not allege that the government of Israel or anyone acting on its behalf violated U.S. law.