You can also think of it as: the guards know you will pay, so they'll try to extract more and more money from you, just as people do in real life.
I have no problem with such concept ...
I just have to ask, how exactly they know? O_o
Did the first guard come to them and said: "Hey dudes i just got bribed by that guy who murdered Steven ... ask for more money next time he kill one of us!"
Nah ... by the model you suggested, they "just do" ...
You kill some guy in the valley, single guard see you, and in that very moment whole freaking town know that you are murderer!
Then you bribe that single guy who saw you ... and in that very moment whole freaking town know that you are exploitable person, and kindly forgets that you killed somebody.
Thats what i dont like about it.

So ... yeah, exactly as you said:
"As for the point about realism/reasonable-ness, its a bit hypocritical."

You want one aspect of the system to be realistic (money not disappearing) but you like the fact that the other aspect is unrealistic
On the contrary.
I want them both ...
I was just coming out from that described situation instead of thinking about some other scenario. :-/
Premise was clear:
You kill a goblin
> other goblin (singular) see you and wants to arest you > you bribe him
> you kill him > other goblin (singular) see you and wants to arest you > you bribe him
> you kill him > other goblin (singular) see you and wants to arest you > you bribe him
> you kill him > other goblin (singular) see you and wants to arest you > you bribe him
> you kill him > other goblin (singular) see you and wants to arest you > you bribe him
etc. ...
That was the situation we got, that was the situation i was working with.
No yelling mentioned, no other withnesses mentioned, no futher cooperation with other guards mentioned.
> Therefore (and i would say logicaly) none of them was included.
In a "reasonable" world, the guard or merchant would shout "Stop! Thief!" while coming up to you, and everyone around you would hear this. And because people are nosy, they'd then watch you interact with the guard, put something in his hand, and then walk away. If the crime was murder, everyone would immediately know (or at least, there'd be rumors that) you're a murderer even if you successfully bribe the guard.
So ... you are saying that once i kill a guy ... in this particular case a Goblin, meaning most likely a guard ... and other guard will see me ... they start yelling "Murderer! Murderer!" ... and then calmly approach me completely alone and accept my bribe?
While whole town, all other guards and everyone around watch this bcs of his yelling? O_o
We most likely live in different reasonable worlds ...
Bcs in my world, if you get to the situation where you even CAN bribe the guard(s) its in such situation, where NOBODY except them can know about your crime ... bcs if there would be any withness, that bribe could mean problems for them in the future.
Obviously the more guards, the higher the bribe ...
But once they start notifying others for your crime, no matter what crime it was ... bribing is no longer a question, unless it happens in jail.
And since bribing was the point of this topic, it have to be possible. O_o
I would be fine with the suggestion in your last paragraph, where guards call for the others as reinforcements.
Great.

But this would require that said guards *actually* are a force that could win against yours
Wich is never the case in Baldur's Gate III. since we can wipe out whole goblin camp quite easily as we both know ...
Funnily enough, still Goblin guards are trying really hard to appear as "force that should be recognized".

and that the money, once deposited in the garrison, it not trivial to immediately re-acquire.
Disagree ...
Triviality of tasks is subjective and not every guard in the world can afford safe by Gringotts.

I would have no problem if that goblin would just speedrun somewhere out of the screen and dig it there, or hide it in some hollow tree ... after all, they are selfish, greedy and not so smart creatures. :P
It also requires that every location have multiple guards and a garrison to do this.
Only if you take it litteraly.

This is a bit too much realism to put in a game that is not centered around thieving.
As i said abowe, personaly im quite fine with this "exploit" as it is ...
As long as it is allways single guard who notice you.
To make it more realistic (and keep it easy, since as you said this is NOT primary goal of the game).
Larian could in my honest opinion try to include some invisible roll for every guard if they will accept bribe ... or if we will be so unlucky so they would be greedy and ask for double ... or even worse, we will be so unlucky so we meet some honorable man, who will get offended when we try to bribe him.