I think I created a bit of confusion with my previous post on this topic, so I thought I'd try to better explain what I mean. In my opinion, a shill is someone fundamentally dishonest who creates a fake internet persona to sell you some product or ideology. I'll give you a couple of examples which (please keep it in mind) are pure fictional in nature.
Imagine somebody starts a blog saying they are a Christian homeschooling mother of 4 and will share their daily life with you. The target audience of this blog will be obviously women in a similar situation (Christian, homeschooling etc). The blog is quite successful and after a couple of months has a certain number of readers. Then the supposed blog owner starts telling you that though her life is hectic at times, there is a certain brand of supplements which helps her to pull through and that they are produced by a Christian company and if you buy them, you'll help all Christians and homeschoolers out there.
Then later you find out the supposed lady was a single guy in his twenties who sells supplements online.
Now imagine that by some reason, I hate Christian homeschoolers and want to give them a bad name so I set up a blog calling myself a Christian homeschooling mom from Arizona and will expressly state that my blog exists to support and promote homeschooling and then I'll proceed with publishing stories which will be ever so slightly over the top, portraying my imaginary family as rather dysfunctional and unpleasant, with spoilt kids, borderline abusive husband etc etc. A normal person will read it and think that home educators are crazy and should be avoided at all costs. So my objective of discrediting the homeschooling movement will be achieved.
There is a difference between a shill and someone who is convicted about a certain issue. There are plenty of Christians who will belong to a certain church and think it's the best. Some will even go so far as to state all others are heretics. They may be misguided in some things but they are sincere and moved by the desire to warn others and to promote their own church/community. They will tell you to join this or that religious group because it's the closest to the Scriptures.
A shill, on the other hand, would pretend to be a sincere Christian and then go around bashing all existing churches, communities and preachers without pointing you to any healthy alternatives as to leave you in the state of despair. (Or sometimes they will point to themselves as the only ones in the possession of some truth which will save you. In this case, it may be not really a shill but simply someone who is very full of themselves and likes cult-like following. ). You see, he's pretending to be one of you and to help, but in reality, such a person is something totally different.
It's much easier to do online due to the relative anonymity of the internet, so it's always a good idea to practise some discernment:)