Has anyone ever worked for a bookie on the credit side of the business?
What party has been given is in effect a credit bet.
Let's look at it like that.
So you're betting "on the nod" and your horse/dog whatever runs a place and pays $4.90. You go to collect and you will have $29 in your name. The $49 less the $10 each way. No actual money has changed hands and you now have $29.

This is pretty basic stuff, and doesn't depend on how you look at it.

If anyone wants to pay more, can I have an account with them please?

(Just remembered I had a free $50 bet today which went on @ $26. If it won I would have been in credit $1250, not $1300.)