It is possible to auto-assign a specific listing type to a membership plan so any members who sign up for that membership plan will have this setting pre-selected. To accomplish this, navigate to Finance >> Membership Plans and click Edit on preferred membership plan:
And search for the wording "pre-select listing type" in the search module and select the preferred option under the Pre-select Listing Type setting:
This will pre-select the listing type when a member signs up for this specific membership plan but these members still will be able to change their listing types later on via their Member Dashboard.
To not allow members to change their listing type, first, identify the Contact Details Form being used for this membership plan under Member's Dashboard tab and click on Edit Form:
And customize the form to change the Type of Field of the listing_type field from Dropdown List to be Hidden Field:
Pre-selecting a listing type via membership plan and making this field a hidden field will make sure these members will always be a specific listing type. This can be a very helpful workaround if a membership plan is dedicated to only businesses.