Pinkie Pie woke up early one morning, and Celestia had not even gotten her sun up just yet. Actually that is more than an hour away; but this would not be important, right now.
She had found herself with a straight mane, and a few gifts too many left by her bed. She knew the gifts had to be delivered, and before the sun hit the horizon.
Presenting herself as Diane Pi, she is posing as a sales woman; but with the intent to present a product as a gift to spread joy and cheer amongst the people, rather than actually making a kill on the sales in the first place.
Naturally, she does give them a means to reach her; just in case they would choose to buy more, without any obligations on the recipients or future customers part. She had stressed this, a bit farther than expected.