You can use this article to see how customers, guests, and subscribers are handled across our Commerce flow connectors:

Handling your contact types

You can use the information below to see how your contacts are labelled and handled:

BigCommerce

Customers
Customers are the users that have an account in your store, including those who haven't opted in to your marketing. This includes contacts who check out as a guest.
Guests
Guests are synced into the Customers list.
Subscribers
Subscribed customers are customers who opted in to receive your marketing messages when they created an account or when they checked out a product from your store. Since our 19three release, this includes subscribed customers who subscribed using the newsletter signup form.

Customers
Registered contacts that have a customer account.
Guests
Email addresses from an order placed by a guest at checkout.
Subscribers
Contacts who opted into a newsletter subscription on your site. If a subscriber unsubscribes on your Magento site, we remove them from the Dotdigital Subscribers list. The contact isn't suppressed.

Customers
Customers are users who have an account in your store, including those who haven't opted into your marketing. This includes contacts who checked out as guests, but only if the guest has opted in to subscribe.
Guests
Guests are synced into the Customers list.
Subscribers
To enable subscriber synchronisation, you need to create the Accepts Marketing field in Salesforce Commerce Cloud. If a subscriber opts out in their store account, they are removed from the Subscribers list in Dotdigital. The subscriber isn't suppressed.

Customers
Customers are users who have entered their email address on your site, but who may not have opted in to your marketing. This can also include users who check out as a guest.
Guests
Guests are synced into the Customers list, and, if they are opted in, the Subscribers list.
Subscribers
Subscribed customers are customers who opted in to receive your marketing messages when they:
- Created an account
- Checked out a product in your store
- Used the newsletter form provided by Shopify
- Have Shopify's Accept Marketing set to True
If a subscriber opts out in their store account, they are removed from the Dotdigital Subscribers list. The subscriber isn't suppressed.

Customers
Customers are users that have an account in your store, including those who haven't opted in to your marketing. This includes contacts who check out as a guest.
Guests
Guests are synced into the Customer list.
Subscribers
Subscribed customers are customers who opted in to receive your marketing messages either when they created an account or when they checked out a product in your store. If a subscriber opts out in their store account, they are removed from the Subscribers list in Dotdigital. The subscriber isn't suppressed.

Customers
Customers are users that have an account in your store, including those who haven't opted in to your marketing. This includes contacts who checked out as a guest.
Guests
Guests are synced into the Customers list.
Subscribers
Subscribed customers are customers who opted in to receive your marketing messages, either when they created an account, or when they checked out a product from your store. If they opt-out in their store account, they are removed from the Subscribers list in Dotdigital. The subscriber isn't suppressed.