Surely, there is no way to guarantee an estimate. Anyone who thinks there is a way is either bonkers or does not understand the English language.
I'm not sure that any lowering of estimates would solve problems.
Could estimates soon take this form? " From statistics gathered from many sources, we guess that for lines of a similar distance from the.......... on the service requested will be around.........maximum, or less. This does not take account of peculiarity either of the line to you premises, or matters within".