Jeff Foxworthy has a funny list of things that, if true, "you might be a redneck." Here's another list, and if enough are true, the group you're concerned about may well be a cult. It seems easier to describe than define what a cult is, so here's a checklist...
1. A strong, dynamic leader, upon whom the group was founded, or who has taken up the mantle of leadership; often one who claims divinity, or who claims to be closer to God than his/her followers, with special authority and anointing.
2. New, original, extra-Biblical revelation, exclusive to the group, teachings hidden from the rest of Christianity (often written by the cult-founder).
3. Elitism, exclusivity, superiority, a “we’re the one true church” position, with “all the answers.” They are selling a particular brand of faith, and they regard other brands as the opposition. All other groups are wrong and their leaders are false teachers. The group seems too perfect.
4. Teaches against unity (ecumenism/pluralism), or is all-inclusive to the point of universalism (“all roads lead to God”).
5. A “last days” obsession--a disproportionate emphasis on eschatology (prophecy) along with some unique interpretations and predictions about the “end times”.
6. Extra-zealous, coercive and questionable recruiting/salesmanship tactics…and they rarely begin their sales-pitch with their unique beliefs. Deceit may also be used to win converts.
7. Legalism and/or asceticism--strict conformity in dress, social restrictions, rigid rules of behavior--as a means of gaining or retaining God’s favor.
8. Total commitment and childlike submission to group authority expected of members, along with unquestioning acceptance of the group’s doctrines, policies, and leadership. The group encourages followers to put their activities ahead of all other commitments.
9. Intensive indoctrination, demanding exclusive/excessive amount of time from members; authoritarian, oppressive leadership.
10. Persecution complex/paranoia.
11. Salvation by works (deeds), as opposed to the Christian doctrine of justification by grace.
12. Defective Christology--denies the deity and/or humanity of Christ.
13. Defective teaching on the Atonement, i.e. the blood sacrifice of Christ as the basis for forgiveness.
14. Communal living (Utopian Socialism), along with the loss of personal rights and possessions.
15. Conditioning, brainwashing, grooming, peer pressure, manipulation.
16. Individualism discouraged / suppressed--the loss of personal autonomy, dignity, and freedom.
17. Pressure to sever family ties; suspicion of family contact. Followers are unable to place phone calls, receive letters, visit with old friends, or to discuss their thoughts with people outside of the group. Such contact is viewed as a threat to the group.
18. Secrecy and isolation, often coupled with survivalist mentality / practices.
19. Personality and behavioral changes in members, often including name changes.
20. Subjectivity--truth is based on experience, feelings, and circumstantial events.
21. Lack of historic perspective--they ignore the last 2,000 years of church history, claiming they alone are the one-and-only true Church, and all previous groups are in spiritual darkness.
22. Combative, militant opposition toward anyone outside of the group.
23. Financial exploitation of members, often requiring the turnover of members’ assets (especially prevalent in commune situations).
24. Requires or prescribes changes in diet/nutrition to influence members (part of total control).
25. Sleep deprivation--fatigue in order to break down resistance to indoctrination, making converts malleable.
26. Chanting ritual, constant repetition of teachings, in order to block rational thought process, keeping recruits from appraising the teachings of the group.
27. Isolation of recruits, who are not permitted to leave the group compound--a greenhouse scenario, effectively shaping the environment, blocking contact with the real world.
28. Conformity of dress--a uniform, habit, or strict dress code, which makes members easily recognizable and set them apart.
29. Unique rites and rituals, often conducted secretly or privately.
30. Ex-members are ostracized, shunned, condemned, or even persecuted (sometimes even murdered).
31. Few external, hierarchical controls, resulting in a lack of accountability.
32. Unique interpretations of Scripture, teachings that set the group apart from the mainstream and general consensus of religious thought.
33. Non-Trinitarian doctrine, denying that God is a Tri-unity / Three-in One: Father, Son, and Holy Spirit…co-equal, co-existent, co-eternal.
34. Requires unquestioning acceptance of their beliefs. Doubts and disagreements are not welcomed; they’re a sign of weakness. Such groups also make claims they can’t fulfill.
35. Any group that promotes itself and its founder/leaders more than it promotes God. They may talk about God and claim to promote faith in God, but when forced to decide between their organization and a God Who is bigger than their group, they will side with their group.