Greetings!

I am working on a economy system for a playerworld and I found one problem:

It would be the easiest and most logical way to set every players individual amount of currency with clientr variables.
But I am not sure how safe they really are, even though they can only be edited on serverside...

Is using clientr variables a good idea?
Or does one of you have a better tip on how to do it?

Thanks for the help =)