Buyer accounts are free on SP with one caveat:
* buyer must have an order from seller in sold status within a 1 month timeframe OR make a coins purchase *
If no orders have been completed within a 1 month timeframe OR no coins are purchased, the account will go into 'inactive' status which will require a subscription or coins purchase to reactivate active status. If buyer completes at least 1 order per month, a subscription is no longer necessary and may be canceled to enjoy free membership.
Alternatively, if a buyer chooses, he or she may become a premium member and avoid the inactivity period completely.