As a delivery driver, do I need to smile when I pick up and deliver a package?

One simple smile. a 'hello or Good Morning/afternoon - as the case may be' and additionally, a tip of your hat to the lady receptionist goes a long, long, long .......................... long way.

Of course. Do it, see how things fall in place for you. That's the trick of the trade.

Yes it is just good etiquette. they are buying your house buddy, thank them and smile.

You stand a better chance of getting a tip at Christmas time if you are friendly and smile.