Ok, so by reading some posts, anyone can sell anything regardless of CE compliance, just by selling it as a kit (even an "idiot proof kit", like a complex board to be finished with only one or three components still to be soldered).
If this would be true, even if you sell something that once assembled will crush every tv or radio signal in your neighborhood due to its emissions, you would get zero troubles from the autority, since you sell it as a kit.
I strongly don't think so. Kits are not a solution against CE compliance.
When you sell a "final" product, so a device that once built can work without the need of other than a power source, you are selling an apparatus, that must be CE.
If you sell a part, something that once assembled it's not for a final use, but it's only something that will be incorporated in a device, THAT's the part that doesn't need any CE. It's the final apparatus that must be compliant, and of course only if you're going to sell it.
As a crude example, no one can be sued because is selling you potassium nitrate. You can use it in many ways. This can be identified as a harmless part.
It will be more different if he sells you potassium nitrate together with a pipe, two caps, sugar and coal, with instructions on how to assemble them. This is a no more a harmless part, but an explosive device.