Selling preferencesThe Checkout via setting determines both the buyer's purchasing experience, and your control over the sale. The recommended option is the Shopping cart. This can be set in the admin section > More options (upper right) > Commmerce > Preferences > Checkout via, like so:
Shopping cart (recommended)
Buyers add items to a cart that exists on your website. It allows rules for tax and shipping. Buyers can pay via PayPal, or directly with a credit card via Square.
PayPal, click to buy
Buyers add items to a cart that exists on paypal.com. Prior to March 15, 2021, this was the default setting. It is no longer recommended since it does not prevent overselling.
Mals-e.com, click to buy
This allows you to add items to a cart that exists on mals-e.com, which also allows you to specify rules for tax and shipping. It also does not prevent overselling. Buyers pay via PayPal or credit card.