Depending on your business partnership agreement with vendor, you may need to use split payment method. This is the way of splitting the money for the deal between website owner and the vendor, so that the customer will pay website's share online and will pay the rest of the sum directly to the vendor.
Usually money for deals are processed through a payment system. However, you may also offer paying for the deal by cash or bank transfer. This is when you would need an option for adding funds to user balance. This will work the following way: the customer comes to your office (or makes the bank transfer to your account), once you receive the money you should add the corresponding transaction to user balance on your site, so he/she will be able to purchase your deals from balance.
Apart from setting the payment gateway up, you may need to change the currency of your site. This may be needed if you choose to sell your deals in a different currency. Please check this guide for information on adding new currency.
To improve conversion from visitors to customers and to spare users time on purchasing, we recommend you to enable functionality that processes instant purchases.