How do I pay the merchant?
Any daily-deal website needs to pay the merchants which deals it promotes (unless you try to charge your merchants instead of paying them).
So, how do you pay the merchant? The short answer is "You decide". And here comes the long one.
Getsocio does not impose any restrictions on your business model. The funds from all coupon purchases made on your site come to your PayPal (or bank) account. From there you may use the money any way you see fit.
To pay the vendor you may use any method you have come to an agreement with them (cash, PayPal, check, bank transfer, whatever). It is up to you to decide what amount to pay (and what percentage to keep to yourself). Also you decide when to pay it (immediately after the deal ends or later).
You may pay the merchant for the number of coupons sold. Or you may consider requesting a confirmation from the vendor of the number of coupon-buyers served, and pay only for the served coupons, while keeping funds for unused coupons to yourself.
Overall, there are many options available, and the choice will probably depend on particular deal/vendor. Of course it would be only reasonable to discuss them with the vendor and come to an agreement on payment terms before you run their deal on your site.