Never trust a red or a blue. Kill them or be killed. They will not hesitate to stab you in the back.
I typically go by the philosophy of if you don't engage me I don't engage you by general rule when doing skyshard hunting general non pvp stuff like questing and whatnot in cyrodiil. I sometimes go in delves and I would see other players trying to do the bosses, they are from other factions and I would leave them alone overall, I've left others alone without engaging them. Just peacefully wait for them to leave. But as soon as they engage me I would agro all the enemies to me and utilize the npc enemies into helping me boost and keep myself alive and in a lack of better words utilize them to kill the people that tried to attack me. I've not died once because of this and easily overwhelm anyone I have tried this with. All while having certain enemies like trolls around me that are in between me and the human player so they can't easily get a target on me. Keeping stuff like reviving barrier always going on as well, direfrost's monster set and the resto staff ward ally too just in case. All while every 15 or so seconds doing the radiant aura so I never run out of magicka. But I am not sure why but I find it a bit numbing to kill other players.