I’ve just bught an NVidia video card from Computers and Parts Land (CPL) .
I asked for a PCIe*8 card but was assured that a PCIe*16 card would work. However when I got it home I discovered that it would not fit, the size difference was obvious enough that I didn’t even need to unwrap the new card.
According to the Wikipedia page for PCIe (PCI Express)  it is quite legal to have a motherboard implement a slower version of PCIe but have the full slot width, so a motherboard could have PCIe*1 implemented but have a socket that will fit a PCIe*16 card. The motherboard and the card will negotiate the capabilities that they both support. But there is no requirement to have a larger socket than required to use the capabilities of the motherboard.
The CPL salesman assured me that any PCIe*16 card will fit into any PCIe*8 socket. I presume that he is used to white-box gear manufactured by companies that can save a few cents on the sockets if they make them all the same size. The Dell PowerEdge T105 that I own has PCIe*8 sockets that do not fit PCIe*16 cards.
So now I have to return the card, and the CPL web site doesn’t even give the hours that the store is open, so I have to call them. Sigh.
Update: I returned the video card, first I had a debate with the CPL guy who had sold it to me regarding whether such PCIe sockets exist. He suggested that I had mistaken a PCI slot for a PCIe slot and was not convinced until I showed him a picture I had on my phone. He then claimed that Dell made sub-standard machines for not using a PCIe*16 socket for PCIe*8 connectors – so it was Dell’s fault not his fault for delivering me a PCIe*16 board when I asked for a PCIe*8. He told me that no-one had ever made a PCIe*8 video card. Then he told me that I was lucky to not have a re-stocking fee (they sold me a device that was not what I asked for, I returned it in perfect condition on the same day and I was lucky to not pay them for the privilege). They gave me a credit note for the value of it (not a refund).
I recommend never doing business with CPL if you can avoid it. I will make exactly one more purchase from them, that will be to use the credit note.