What's wrong with you dude? The way you reply to people is super cringe.
That word is enough to trigger me.
Anyways, the trade only playthroughs are mostly for masochists that have billion days a month to play the game.
It would make sense to make some things non-negotiable, and not for sale, be it through marking them in red font color, and not making bargaining available for it, or just not showing it in the trade screen at all.
For example, in Amazing Cultivation Simulator, there's items in trade screen that are marked in red, and when hovered show the reason why you can't trade for this in a tooltip.
Also could make some things tradeable if you've got X relationship with them, are in their faction, or aren't in enemy kkngdom etc.
I'm guessing it's a bug, because 2.7 billion is coincidentally the maximum value of a signed 32-bit integer.
The code posted by Medivhtratos uses single precision floats which go way higher, but there may be an implicit conversion in an operation there somewhere or the variable which holds the value that is actually displayed to the player isn't a float so it's being maxed out. Or, by coincidence it actually is 2.7b and the way to find out is to throw in your known values & see what the function would return.
Unlikely, as the size of a signed short 32-bit int is 2.14 billion, and the OP mentioned 2.7 billion. Unless the amount that the side you're trading with is barred by the size of the signed short int, which would make no sense, since you can't ask for something to be sold for -12000. I did not check the code for that, so I couldn't know what is the problem, if there is any, that is.