Yes, any customer whose preferred receipt format is none and this includes the default Walk In customer will not print a receipt automatically at the end of the transaction.
1. Check and see which customer is the default Walk In customer in
2. Edit your walk in customer in Manage Customers grid and go to settings tab
3. Set to Preferred Receipt = none and save
Walk in Customers will not print receipts by default - you can always change this setting on the receipt itself for times when the customer may want a receipt (printed or emailed) just click the orange 'no receipt' symbol and change it to print or email and you will get a receipt.
You can also default any new 'regular' customer to not print receipts as well by setting Default Preferred Receipt to none in Admin Settings >> Default Settings >> Customer
