Hi,
It all depends on the situation. For example, if a customer has booked a $100 booking with one of the vendors and the booking is successful. After that, when the funds become available, the vendor makes a payout on this $100. And then, when the refund is made, the vendor will have to somehow return the funds back to you so that there are no problems with the balances. But, this is possible if you have manual payouts and, for example, pay vendors once a month after the 15th of the following month, then you will always have at least 2 weeks before the payout to make a refund, if any.