Yes, I understand what you are saying. However, we got tired of it as well, and followed the Triple P methods.
Our reasoning was that if you give a child too many chances, they just end up only doing what you want on the final chance. It leads to just not taking what you want them to do seriously. You aslo need to pick your battles on what is worth negotiating about.
Also, I think at that age the child is too young to negotiate, and it just gives them the chance to push your limits as well.
When its something big, I try and look at it from their point- are they being reasonable? are they tired etc.
I use bribes of course....

and the authoritative voice also lets the child know you mean business.
Often also if you just ignore the back chat it will stop and they will do what you ask- they just like having the last say as well.