RVsitebuilder 7 doesn't support shopping cart feature at this moment.
To add items for selling or renting
You can use Pricing section to add items.
To add payment options
You can use feature "Insert" to insert your preferred payment link as a button. Please see guide to insert button at Inserting Button.
Or add Paypal Buy Now button for Paypal payment.
To add appointment or booking
You can our Online Form and add Calendar field to is. Please see guide how to add Online Form and Fields at Adding Online Form.