The Book of Mormon says, IIRC 2 Ne 9: "Wo unto the liar, for he shall be thrust down to hell." This life isn't always fair, but we can trust Him to get it right in the end -- the important thing is that we are honest and never stop humbly trying to do what is right. I have learned we really can be OK.
Edit: Which doesn't make it easy or less real -- but knowing it really helps me.
Witnesses are straightforward: blackmail multiple members, or get some plants who are "new to the ward". Might take awhile to build up a ward-wide infiltration network, but it's likely worth it.
Hell, we're talking about the same demographic that routinely falls for MLM schemes like dōTerra. Once you get a bit of a nucleus, a ward's espionage machine can very well be self-maintaining and decentralized, using peer pressure and some judicious application of scripture to guilt-trip people into being informants.
As for evidence: that's the whole discussion here :)
> There is also (to us) scripture that says Church discipline can only deprive one of membership
Which is all that's really needed to be effective leverage.