Good first post Generalgym.
The bookies set a market hoping that punters will be stupid/smart enough to back horses at the odds provided. The prices then fluctuate according to market forces, ie punters/owners/other bookies money. Does anyone else get annoyed when stupid racecallers/commentators state that the bookies are keen to lay something or keen to take something on, when in reality the price is only being adjusted because there is no money for it, ie bookies may set the original market but punters or weight of money decide what happens. What's even more annoying is when these so-called experts say the bookies lost a heap on that last favourite because they took it on easing it from (for eg) 1/1 to 2/1. NO, NO, NO, these are the favourites that bookies love to win because there has been no money for them. (unless of course it has been backed SP, but that doesn't happen any more does it, doesn't happen any less either.)
Sorry, getting a bit off track there.