That's what quarantines are for.
The weirdest thing is that 0 influence isn't even that low, a relationship is still considered Neutral down to about -20 or so. I imagine the conversation going like this:
Hydral: Here are a couple pilots I fished out of space after blowing up one of your spy satellites. My bad, I didn't think those things were manned.
Andor: Nope, we mildly dislike you. No deal.
Hydral: I'm not asking for anything, just take them.
Andor: NOPE.
Hydral: Okay, well, the slavers are always buying...
Andor: If you do that we'll hate you forever.
Hydral: Um, so I guess I'll just let them rot in my hold for the rest of their lives?
Andor: That is acceptable.
Hydral: Jeez, it would have been more merciful to just let them suffocate in space. I guess I won't rescue your pilots any more.
Andor: That is also acceptable.