Did you read what he wrote? He said that he has heard of people sending coins and then finding out later that they did not get the same line they thought they were betting. This cannot happen with a post up shop.
Of course this could happen at a post-up book. They can and have done anything they wish, with the added leverage of holding more than your stake. Not sure why you two are so desperately attempting to defend this preposterous position.
For a given bookmaker, you're seriously arguing that you would rather he hold your money than you hold your own money? Lulz, the full-blown Stockholm Syndrome present among sports betting ploppies never ceases to amaze.