If you think more carefully about what the OP wrote, you might just understand that it's not so much querying prices, as wondering about how other tradesman go about charging their clients for work, without first verifying they they'll be happy with what gets done or charged, no matter what the final price is. If I ring that garage for a car service, they'll tell me the cost of the service and what's going to be done, and they'll ring me to advise me of anything outside the original remit, and then discuss the revised price - neither of which the engineer in question did.
And there are a lot more things discussed on this site than just DIY