Questionable billing practice

I have used Burgess and Partners on several occasions and the work done is good, however the billing system is questionable depending on the Team sent to your site. Once the job has been inspected, they leave to go and purchase item/s required to complete job. This shopping can take time and I was recently charged for the shopping time plus the 20 minutes it took to complete the job on top of the call out fee. This is not stated clearly in the billing process and times of arrival and departure are not stipulated so make sure to do this yourself. A very simple job can be very pricey! I called the Company to clarify the billing process as I would like to continue using their skilled team in the future. I have had no response.