There are a few exceptions to the general rule that you shouldn't expect to pay someone else to give them rights in connection with your own movie (see previous FAQ). For example, the very top sales agents charge a fee of $7,500 to $15,000 for the privilege of having them represent your film at the top film festivals and elsewhere. This is really a screening mechanism to weed out the amateurs, as top sales agents have access to the top studios and they are highly sought after. They invest enormous amounts of their time, credibility and promotional activities to get the films that they represent into the right hands.
If Cinetic or Film Sales Company or a sales agent of this caliber offers to represent your film, then you should beg, steal or borrow, but find the money to make it happen. If any other sales agent seeks an advance, make them first demonstrate what they've done for other similar films lately before considering paying any fee for their services. A straight commission in the event that they actually find you distribution is generally more appropriate.
Another exception is in the case where a home video/DVD-only distributor seeks an advance from you. The top distributors in this market have access to major DVD retailers such as Blockbuster, Target and WalMart. If you want to get your film into these lucrative distribution channels, you are in very good company. Market forces permit the distributors to charge you up front for the privilege.