Nevada gaming regs prohibit sports books from taking wagers on teams where there's an ownership conflict, meaning that the company that owns the book also owns a share of the team in question. This has been the case with Caesars Palace and the Boston Celtics for years (Bally's is a part of Caesars Entertainment). Similar situations exist at Silverton with the LA Lakers and at the Palms with the Sacramento Kings. We're not sure why William Hill didn't have the Celtics lined, but there may be a similar ownership situation at work, either with Will Hill or in the outlet you were checking.
When a team isn't included in a futures pool for this reason, the highest placing team is the one that wins. For example, if you bet the Oklahoma City Thunder and they lose to the Celtics in the NBA finals, your Thunder bet is a winner. In fact, if you have the Western Conference champion on the futures line and the Celtics make it in the East, you're a winner before the first tip -- just assume the Celtics don't exist.
Keep in mind that futures bets carry big edges for the sports books, often 30% and up, so they should be played sparingly and for low amounts, if at all. However, if you want to make a futures bet like this and find the same price at Caesars as you do someplace else, make the bet at Caesars where you're getting the same odds with one team already elminated.
