“Now I beseech you, brethren, mark them which cause divisions and offences contrary to the doctrine which ye have learned; and avoid them.”
Romans 16:17

Notice their description- they would eventually cause division and bring forth doctrines, teachings contrary to what you have received, meanwhile the Bible says:
“Nevertheless, whereto we have already attained, let us walk by the same rule, let us mind the same thing.” Philippians 3:16
As much as you have attained in your local assembly, he says walk by the same rule, be of one mind, he gives no room for such contrary behaviours and those who espouse such have made it clear that even though they are in the midst of brethren; they should be marked (observed) and avoided. In most cases, they are the exact expression of this verse:
“Also of your own selves shall men arise, speaking perverse things, to draw away disciples after them.” Acts 20:30
Manipulating those they consider simple in order to take advantage of them, set themselves up as masters over them in everything:
“For ye suffer, if a man bring you into bondage, if a man devour you, if a man take of you, if a man exalt himself, if a man smite you on the face.” 2 Corinthians 11:20
Do God’s word and avoid such people. If you hear things contrary to what you’ve been taught- be like the Apostles and the churches of the Gentiles- ask your immediate leader or Pastor just like they asked Jesus and the Apostle Paul respectively.