What It Means To "Buy" A Number
You can wager on a specific number at any time and get true odds on it. This is called "buying" a number, and the bet you are making is called a BUY BET. There is a difference between the "place" bet and the "buy" bet, because the payoffs are slightly different. Of course, we're talking about these numbers being rolled in relation to the seven being rolled.
Number.... "Place" payoff.... "Buy" payoff
4 or 10 .... 9/5 .... 2/1
5 or 9 .... 7/5 .... 3/2
6 or 8 .... 7/6 .... 6/5
As you probably notice, the payout on the "buy" bet is higher. In fact, these bets pay the actual or "true" odds of them being rolled. However, it still comes with a price. To take advantage of those true odds, the player has to pay a commission to the house. The commission is 5% and it is derived out of the potential win on the bet.
For example, let's say you made a "buy" bet for $50 on the four. If the four was rolled again before the seven, you would be paid off $100 for the win. You will fork over a 5% commission, or $5, to the house when you make the bet. Just as in the case of the lay bet, you will have paid this to the casino, whether you wind up winning the bet or not.
The reason you're paying a commission is that unlike the Pass or Don't Pass bets, you are getting true odds and can lay this bet down at any time after the point is established.
If you want to be able to place these bets you have to check out this list of online casinos.