All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
It is not permissible for a person to excuse himself from paying taxes to a government if the government has imposed these taxes in order to provide facilities or services to the public unless this government has a sufficient source of income to spend on social welfare, and there is violation of public treasury. From these details one may find out the answer.
Know, dear brother, that backbiting is prohibited except in six situations.
Here are six instances where it can be permitted.
1. A report for the redress of some injustice, wrong, tyranny or high-handedness in which an oppressed person can petition the King, the judge, or a person in authority, against a person who has perpetrated such offenses.
2. To seek help to stop some practice or work which may be against the principles of religion.
3. To seek a ruling (Fatwa) on a specific topic from a qualified person in authority.
4. To caution the Muslims about the evil consequences of some mischief.
5. To inform about someone who indulges in evil practices openly, for example publicly drinking liquor, treating people cruelly, causing usurpation of their property, and imposing and collecting taxes with cruelty.
6. To introduce someone with nicknames such as lame, deaf, blind, squint-eyed when such a person is already known by such a name. In this case, his introduction with such nicknames is permissible. But to use such words to humiliate such a person is forbidden. If he can be introduced in a more dignified way, then it is better to do so.
Based on the above details, there is no harm to inform your friend about a person who is a cheater etc. Know that this information should be limited and not reach the extent of defaming him or referring to his shortcomings.
If you mean from making Dhikr (mention of Allah) in a group that some Sufis practice, such as getting together, reading poems paying tribute to the Prophet and other saints – as they claim – or repeating the Names of Almighty Allah constantly as one of them say “Haq, Haq”, and the others follow him and repeat after him. Sometimes they repeat “Hu, Hu, Hu”, and during this practice sometimes they hold their hands together; no doubt, doing so is an innovation and a deviation. There is no evidence for such practices in the Quran or Sunnah. The Prophet said: “The worst of all matters are those that are newly invented; every newly-invented matter is an innovation, and every innovation is going astray, and every going astray is in the Fire.” [An-Nassaa-i]
The Prophet also said: “Whoever introduces into this faith of ours (Islam) something which is not part of it, it is to be rejected and that person is condemned.” [Al-Bukhari and Muslim]
A Muslim must avoid this and all other kinds of innovations.
Allah knows best.