As you say if the customer does not like it, they are free to go elsewhere!
And pay more accordingly for not necessarily any better a service.
attending properties where the client is not allowing any flexibility
We get it with tenants all the time. No flexibility for the annual gas safety check, which is compulsory for the landlord and in the tenant's own best interests. However, it is amazing how quick a morning off, or an early afternoon finish at work can be arranged when there is no heating or hot water. Yes it is a service industry. But most customer facing companies have opening hours.
Does make me chuckle sometimes.
Got half a dozen voicemails to reply to this morning from people that have left messages asking me to respond to emails sent following a phone call. A phone call that included me telling them I was in college all week and would reply when I'm in the office Friday or Saturday.