How can I prevent duplicate submissions when saving form data to Google Sheets?

You can check for existing entries in the Google Sheet before appending new data. Use `SpreadsheetApp.getActiveSpreadsheet().getSheetByName('Sheet1').getDataRange().getValues()` to retrieve all existing data, then iterate through it to see if a matching entry already exists based on a unique identifier (e.g., email address, timestamp). Alternatively, use a unique timestamp as part of the data to inherently prevent duplicates.