There's purchase confirmation even in 80s videogames for home PCs (by PC, I mean, Commodore 64), where it wasn't even a possibility to have a connection betwen real money and game money.
The question is: can the user regain the losses immediately if there was a mistake? If not, how large these losses would be?
There are some cases where loosing fictional money easily was an option, but even then, it was a minimal loss (well, unless we talk about poker or similar):
In Pirates clones, like Port Royale, you can loose money on buying too much of something, but that's actually the point of the game.
In some RPGs (like, Baldur's Gate perhaps... haven't played such for ages), you had to drag-n-drop between the two players to make a purchase, and it was really hard to do it accidentally. In some games, still there was a confirm option in case you decided you want to rearrange your basket. Again, no real money was involved.
So, if accidentally loosing your money because of a sudden move is actually part of the gameplay, then it can be an option to loose your virtual money, but I guess it should be up to the user how much investment could (s)he make to the game.
But if you have to double-click, or slide, that's also a confirmation, no need for pop-ups.