Another HUGE warning sign is when the potential converts or interested people suddenly start displaying group think.
Group think can be misleading, yes. Majority does not make right... sometimes the loudest simply get heard the most. Or... 'that many people can't be wrong'... is applied, which is also a fallacy. Group hate or group disdain would be a huge warning sign too, imo.
At the same time, some who see the same things might also seek out others who see the same. And some who share the same faith, might seek out others who also share the same faith.
One should probably be certain they KNOW the difference, rather than imposing their judgment.
No one should follow another person. Especially not one who says that they should, or that their lives and the lives of their loved ones depend upon you listening to and following them. Beware of people who say such things; including people who say that they are the mediator between you and God (or even you can Christ).