All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If there is a dispute between two people over any matter, and there is no agreement between them, then in this case, they are permitted to appoint a third party to arbitrate between them. Allaah Says (what means): {If you fear a breach between them twain (the man and his wife), appoint (two) arbitrators, one from his family and the other from hers; If they both desire reconciliation, Allaah will cause it between them.}[Quran 4:35] Ibn ‘Abbaas gave this verse as evidence of the permissibility of resorting to arbitration (i.e. appointing someone to arbitrate between two disputing parties).
The rule by which the disputes are solved and come to an end is the following: The proof should be given by the claimant and the one who denies (the allegation) should take an oath. Therefore, the complainant should bring evidence about what he claims otherwise he has no right in what he claims. For more benefit, please refer to Fataawa 83395 and 86011.
It should be noted that if there is no Muslim judge – as it is the case in non-Muslim countries – then the Muslim community should set up a committee of Muslim scholars and wise people in order to judge between people when there are disputes.
As regards your second question, the people who stand in a queue in a commercial store or else all have equal rights, so it is not permissible for anyone to break the queue in order to do his transaction without seeking the permission of all the people of whom he got ahead. Therefore, you should know that you were wrong in pushing ahead of some of them without their permission. Hence, you are obliged to repent and not do the same thing again.
Allaah Knows best.