(confused)!

[chinstrappenguin]

I ordered a CD from eBay yesterday. All good, marked as dispatched straight away. Today I received the item and It was from Amazon. Amazon packaging and slip. Does anyone know what all this is about? Thanks

Check the price you would have paid on Amazon and see if it's cheaper than you paid.
There are some sellers who advertise on eBay and, when buyer pays, the seller orders the item from Amazon as a gift (no invoice) and put delivery address of buyer. They sell for more than they paid and make a nice profit for very little effort.

Is that allowed then?

It's allowed yes, it could be DropShipping or they may also be Amazon sellers who mixed up their packaging. You got exactly what you ordered as requested. Nothing dodgy.

It's allowed by eBay but not by Amazon Prime afaik