There are Aiding rules that administration members are familiar with, but they are currently getting re worked i think so they are not available for general population.
But i can tell you the basics of Aiding rules.
You can only aid a player that was Suspected in a RP you were in.
Meaning if you weren't with him when he was suspected or were not in same RP you cant help him no matter what.
Also regarding /fillup players in the past semi abused this to fillup on move from a mechanic, so in some cases you should not su a player who is lets say parked a a suspect coming in to fillup.
But if you see a mechanic driving in the chase and giving fuel to the suspect 1st /report for interupting rp/cop baiting then you are free to suspect the mechanic
So this are the basics of Aiding, A-team members do try to explain this and many players know how to Aid in the right way, if you see players aiding in a wrong way inform him that he is rulebreaking and /report if he keeps doing it.