Some customers are just pain in the rear fickle, changing their minds frequently...
Others just genuinely forget to mention an extra bit that needs doing...
Or while doing a job you may notice an improvement that could be made..
ALL businesses have unforeseen circumstances and factors crop up...
Some can be covered by your initial costings.. Others have to be an increase charge to the customer..
e.g. Shops ramp up their prices to cover losses due to shoplifting..
We may not get shoplifters, but at some point an item you supply may fail prematurely needing warranty replacement...
And although you might get a free replacement rom your supplier..
You have got to cover your labour and travel expenses for this replacement work..
So make sure your initial costs cover a bit more than the bare minim assuming the whole job goes perfectly to plan.
Guinness