It is no different in sports betting, even if you can’t negotiate on the opening number.
The opening number is always the starting point and you can almost always determine whether or not it will go lower or higher based on what that initial number is. In a negotiation, the first person who says a number generally loses. There are always two options when facing this issue and they are walking away and finding a lower price somewhere else, or trying to negotiate a bit on the price if possible. We’ve all been in a situation before where we tried to buy something but the price just wasn’t right.