I don't qoute a price over the phone.
I charge a trip/diagnostic fee to come out.
I look the job over and present the price to the customer from the book. There are adjustments listed in the book such as exeeding a certain ceiling height. If these conditions exist they are added to the price of the task.
If the wiring that I'm connecting to needs to be repaired or replaced than there is a seperate task for this.
So I would show the customer the cost for repairing the wiring and also the cost for the receptacle installation and get a signature of approval before I begin any work.
If the customer declines to have the work done I collect the service/diagnostic fee and leave.
The prices I mentioned ealier do not include the service/diagnostic fee. I currently charge $39.50 for this so that would be added to the price.