How do you know the information you are getting is reliable? Usually something within you will tell you. Often I get asked to verify a source to determine whether or not he/she is a shill.
Shills, also known as agents, are people who are working for the system and not disclosing it. These people are everywhere at every level and they are planted to mislead you through distraction while simultaneously giving you drips of truth. They will keep you entangled in a web of pseudo-truth to keep you partially satisfied yet always craving more, going back to them hoping for answers they will never give.
Shills serve a purpose. They are gatekeepers to protect the truth as the truth in the wrong hands breeds disaster (just look at this place). Only those worthy will pass. You have to do the work in order to know who is lying to you and who is not. This is part of the process. Shills will filter out those who see a bit of truth from those who see more. If you are content to stay at a certain level of truth, you will not progress. Only those who are committed to the path/the way will have access to higher levels of truth.
The above video was created as an overview/introduction to shill-spotting and as time goes on, some of the points may change such as subscriber count because more people are awakening, but it is still a valid guide on how to spot shills. Some argue you can never really know, but that's not true. Some are harder to detect than others, but you certainly can know.