Netstat will not help you detect sniffers.

Sniffers are generally completely undetectable. There was another thread about making them undetectable - it is generally very hard to detect them anyway.

If you control the upstream traffic (i.e. you are the ISP), it's possible to detect sniffers under some circumstances, but you won't be able to detect your ISP sniffing you.

An ISP is ideally placed to monitor IP traffic in any way it sees fit. It doesn't need ethernet "sniffers" in promiscuous mode to do this because all the traffic goes through its routers anyway - it can just instruct the routers to send copies of packets to a given destinatinon.

Anyone who says they can see their ISP sniff the network is lying. ISPs can do this easily and without any possibility of detection.