When a new order comes in, FarApp determines whether or not to create a new customer in NetSuite by searching for customers based on a combination of the email and name/company name of the customer on the order. These requirements may vary depending on your specific account configuration.
If FarApp can't find a match using the customer data on the order then, it will automatically create a new customer. If FarApp finds multiple customer records that match the customer information on the order it will match to the oldest (by created date) customer record.
Note: When a customer matches on name/company name but not email address, a new customer record will be created. If the customer ID (aka entity ID) NetSuite automatically creates for your customers is composed of the first name and last name (which is the default), then FarApp will append the customer ID with the order number since NetSuite requires that all customer/entity IDs to be unique.
For example, if the customer "Bob Smith" on order 17363 matches to an existing customer "Bob Smith" in NetSuite but the email address for the existing customer differs from the email address on the order, a new customer record will be created with the name Bob Smith  in order to make the customer/entity ID on the record unique.