3rd Party Checkbox on Prospect Form
The prospect's 3rd party marketing check box is NOT considered/evaluated when ANY Marketing emails are sent. It is a REFERENCE field of information only.
Some shops sell lists of prospects. They would use the QUERY report writer to generate a list, exporting to eXcel to hand over to a 3rd party company, like a photography. You would use the status of the 3rd party checkbox to know whether is is OK to include the customer info in the data being provided a 3rd party.
Marketing/Prospect Lists you import are typically purchased and you could not legally provide to a 3rd party which is the reason the 'Receive 3rd Party Info' is left unchecked on list import.
So it does not matter if the 3rd party marketing is checked or unchecked for a SHOP's marketing efforts. The shop is not the 3rd party.
Legality, the Customer = First Party, the Shop = Second Party and when the Customer provides their personal info to the shop then they are opting into communications and marketing with the shop. If the shop considers providing the customer info to another company, like a photography (a 3rd party), then the store should ask the customer for permission to share. Based upon the customer's answer the shop should set the 'Receive 3rd party' info accordingly.