I strongly recommend that you do not order from whinkel. My experience, which I will share below, is the same as many others have described in their online reviews. If you think, "oh, but they got such a good offer"... well, chances are that they actually don't. I don't want to make claims that may get me in trouble, and therefore will only state that what this shop does should not be legal. Keep reading.
I ordered an expensive graphics card for more than €800 and paid in advance via iDeal. According to their website, it was on stock and would be shipped the next day. Instead, I received an email from them the next day, asking me to call them. When I did, I was informed that the card is not actually on stock, and won't be for the next three weeks.
I then asked to cancel the order. The guy on the phone didn't want to cancel it and suggested to send me a different card for which I only had to wait "a few days". I declined and informed them that I was going to order the card I wanted from a different shop; the website of the other shop indicated that they actually had the card on stock. The guy on the phone then tried to convince me that the other shop didn't actually have the card on stock either, even claiming that he called them while I was waiting for him to "talk to somebody".
I insisted on cancelling the order. The whinkel guy on the phone then told me that in that case, I would not get my money back for the next 14 days and basically implied that I wouldn't be able to afford to order elsewhere before they refunded me. I still insisted on cancelling the order. After about twenty minutes, the guy finally relented and confirmed that the order was cancelled.
I then immediately ordered the card from the other shop, and they promptly delivered it the next day. It seems that wrongly claiming to have something on stock in order to trick customers into paying in advance isn't as common as the whinkel guy on the phone seemed to suggest.
After 14 days, whinkel had still not refunded me, so I wrote them an email (in Dutch, actually, but I had a Dutch colleague proofread it). They did not reply, nor did they refund my money. After 19 days, I contacted thuiswinkel (where whinkel is a member for some reason), and they then contacted whinkel on my behalf. Whinkel then finally confirmed that they would refund me, which they indeed did a few days later. So, about three weeks after my attempted purchase, I finally had my money back.
This experience seems to be common when you look at the other reviews. The only positive thing I can say is that the guy on the phone was willing to speak English with me, so I didn't have to rely on my crappy B1 level Dutch. Still, given the experience and the fact that it appears to be a common strategy, I strongly recommend that you ignore any listings by this shop. If you can't resist, at least pay with credit card or paypal so you don't have to worry about your money.