Regarding How did Malfoy feasibly manage to buy Peruvian Instant Darkness Powder from the Weasleys? I pose a question: is there a canon occurrence of shoplifting? I do remember Harry stealing a lollipop in the HP3 film, but that is the only one I can think of.
Yes, shoplifting does exist in the wizarding world.
George warns a boy in their shop not to try stealing anything, which implies there is some amount of shoplifting in the wizarding world.
“Fred’s twin shook Harry’s hand energetically. ‘Giving him the tour? Come through to the back, Harry, that’s where we’re making the real money – pocket anything, you, and you’ll pay in more than Galleons!’ he added warningly to a small boy who hastily whipped his hand out of the tub labelled: Edible Dark Marks – They’ll Make Anyone Sick!”
- Harry Potter and the Half-Blood Prince, Chapter 6 (Draco’s Detour)
The boy seemed to be attempting to shoplift the “Muggle” way, by taking an item and attempting sneak out of the store without paying, hoping no one would notice.
There’s also a spell called the Thief's Curse, which seems clearly intended to stop theft.
“By buying this book — and I would advise you to buy it, because if you read it too long without handing over money you will find yourself the object of a Thief’s Curse — you too will be contributing to this magical mission.”
- Quidditch Through the Ages
If theft wasn’t still a problem in the wizarding world, spells like that would be unnecessary.
In the PlayStation game, it seems like you can steal things as well - Harry breaks into Magical Menagerie to get Ginny’s brass scales. He sneaks around in the shop and then takes the scales while avoiding the owner who told him to leave.
Magic can be used in thievery as well. The spell “Alohomora” actually originated from a word from West Africa that means “favorable to thieves”. J.K. Rowling clarified this in court while suing RDR Books.
Q. Could you give the Court an example.
JKR: I could give several. But Mr. Vander Ark gives an etymology for alohomora, which is an incantation used within the Harry Potter books to open a locked door by magic. And he asserts that this word was derived from the Hawaiian aloha meaning good-bye. Which is errant nonsense. Alohomora is a Sidiki word from West Africa, and it is a term used in geomancy. It is a figure -- the figure alohomora means in Sidiki "favorable to thieves." Which is obviously a very appropriate meaning for a spell that enables you to unlock a locked door by magic.