Formal:
* Cunning
* Craftiness
* Deceitfulness
* Duplicity
* Machiavellianism
* Artfulness
* Slyness
* Subterfuge
* Wiles
Informal:
* Trickery
* Shrewdness
* Cleverness (in a negative sense)
* Dishonesty
* Sharp practice
* Double-dealing
The best synonym to use will depend on the specific context of your writing.