1 Of course, the money. The cost of entry (free of charge, one-time fee, annual fee). The cost of the lid - payment for the lid, for the transaction, as a percentage or money. If per lid - when is the payment made upon receiving the lid or upon receiving money from the customer?
2 Responsibility of the agency: do you receive the lid and are accompanied/ helped to sell/rule problems or just throw your phone/mail/name/hostel? In the first case, the benefit is clear, in the second, you will have a very low conversion: a person has come to a large agency, and his "football" to several smaller players, they say, you can not afford us. And everyone needs to explain their task anew.
3 Types of lids that come, and the second important - competitiveness (the ratio of the number of lids to the number of studio partners that take them). Are there restrictions - no more than three partners per lid, for example?