IN BEFORE - Some poster says "just run away and LoS them"
just run away and LoS them
1) Find a pole, or corner, or anything that blocks LOS
2) Stand near it
3) Use instant cast ranged attacks on sniper
4) When you see his cast bar start to move, step behind cover
5) His casting bar says "Failed" because you LOS
6) Step out and attack again
7) Go to step 4
You will test their patience since they wont be able to hit you with anything that's channeled.