Hi! Why don’t you offer the client two options at the starting of the project?
- Full site tweaks.
- Partial site tweaks.
If the client chooses a partial site tweaks, do only the agreed amount of work. If the client asks to implement additional functionality, then you can refer to option 1 and partially revise the budget.
There is a third option. Don’t take sites for revision and correction 
Personally, I choose this option and now I have no problems with clients.