Best Way to insure the success of a Spy?

[80k]

My friend tried to place a spy in a rival civ and they immediately declared war on his civ. I tend to hesitate doing spies until/unless I go communist, since the spies are more experienced.

What other ways besides communism will help raise the chance of successful spy missions? Does being technologically advanced have anything to do with it? Any other factors i should be concerned about?

Thanks!

 

[Strider]

Well, paying the large sum of money for safely is a good bet.

 

[kb2tvl]

I think being allied with them helps get a spy in.

 

[80k]

yep, i always do it "safely". i really like the spy features but always hesitate to use it until i go communist.