The fact that there's no flinch when snipers get shot is the biggest joke in this game. Snipers are so incredibly over-powered it's ridiculous. In conclusion, fukk snipers.
There is no flinch period. Correction, there is flinch but it doesn't affect their aim. I've seen killcams where I'm clearly shooting first and they are flinching with a blood red screen but they still manage to kill me. Also, It doesn't help that sniper guns have no recoil or bullet drop.