Here is how you know if someone is a leftist shill: ask yourself this: Does (whatever they are saying) help Republicans or does it help Democrats. If it helps Democrats they ain't on our side or they aren't helping. If they say they are not voting Republican they are not helping even if their intentions are genuine.
There are going to be times where we have to suck it up and do something pragmatic that you may not be 100% satisfied with such as voting for a candidate who is a RINO. The best thing to do is suck it up, vote for the RINO and get a better candidate next time around in the primaries. It's important we plan for the long haul.
I don't think there are many of them yet but we need to not tolerate this one bit.