To target subscribers based on complex criteria, such as recent engagement and geographic proximity:
Use SQL Queries in Automation Studio to create a highly specific audience segment. SQL queries allow for the combination of multiple data points and criteria into a single query, providing the flexibility needed for complex segmentation.
Write a SQL query that joins email interaction data with subscriber location data, filtering for those who engaged within the last 30 days and are within 10 miles of an NTO store.
Reference: Salesforce Marketing Cloud SQL Query Activity in Automation Studio

For handling multiple values for a subscriber attribute effectively:
Use Data Extensions: Data Extensions provide a flexible and scalable storage model that can accommodate complex data types, including multiple values for a single attribute per subscriber.
Advantages: Unlike Profile Attributes, which limit each subscriber to a single value per attribute, Data Extensions allow the creation of relational data models that can store multiple entries for individual attributes.
Reference: Salesforce Marketing Cloud Data Extensions

To effectively set up a welcome journey leveraging customer data across multiple data extensions in Contact Builder:
Single Attribute Group: Create one cohesive Attribute Group that interlinks Customers to Contacts, Orders to Customers, and Products to Orders. This setup ensures a streamlined data flow and relational integrity, crucial for targeting and personalization within the journey.
Data Relationships: This configuration facilitates the use of data across different stages of customer interaction-from acquisition through orders to product preferences-enabling more personalized journey experiences.
Reference: Salesforce Marketing Cloud Contact Builder

To troubleshoot issues with outdated data from Sales Cloud in Marketing Cloud, the admin should:
Check Synchronized Data Extensions: Navigate to Contact Builder and review the Synchronized Data Extensions. This area shows the synchronization status and configuration between Sales Cloud and Marketing Cloud.
Data Refresh Rate: Verify how frequently the data is synchronized and ensure that the synchronization schedule meets the operational requirements, adjusting as necessary to ensure data is up to date.
Reference: Salesforce Marketing Cloud Synchronization Documentation

To resolve the issue of a data extension not appearing for email sends, confirm:
Sendable Status: Ensure the data extension is marked as Sendable. This setting links the data extension to a subscriber attribute, allowing it to be used for email sends.
Configuration Check: Verify the send relationship within the data extension properties, ensuring it correctly relates to the subscriber key or another unique identifier used for email campaigns.
Reference: Salesforce Marketing Cloud Data Extension Setup