When you get intercepted after making trades, and you allow a scan but then refuse to airlock your contraband, or if you just refuse the scan, the game doesn't warn you that this means war and will set your relations to the faction to -50. Once you go to actually engage their fleet, it does, but unless your fleet is very small, this is sometimes the only option. Once you're in the situation where you've refused you do get a warning about attacking the picket, but you can't go back and be like, actually, nevermind, I don't want war, I'll pay a fine and allow a scan etc. It seems like players should have an idea of what effect their action will take.
It's also weird that these picket fleets will suicidally refuse to let a giant player fleet disengage, requiring you to pop them like a grape and thus ruin your rep. It seems like if the player fleet is small, they should be able to disengage and only take maybe a 20-rep hit (or -25, or -30; just not -150). If the player fleet is big, the picket should stand down because it realizes that standing in your way means guaranteed death and is pointless. Same -20 rep hit and they let you go.