I think you might be convolating 2 different matters. Being responsive is expected in any industry - no one is going to argue otherwise.
Schedule compatability, on the other hand, is a separate issue. Client/ provider may set up his scheduling system however he wishes. Free market and all. That said, every businessmen ought to prepare and frankly expect that not everyone will abide by your system. And the business has the sole discretion whther or not to do the deal.
If you work in service industry, you ought to understand that not every enquiry equal to a deal. Some proceed on mutually agreed terms, some fell through for whatsoever reason. And I totally agree that dealing with multiple 'fee proposals' on daily basis is simply exhausting. But hey thats the cost of running a business. The only way to avoid it is either close down shop or never expand your client base.