If an ordinary person buys one of these lamps from overseas, say via Ebay, or at a local store they don't become responsible for the misrepresentation
You are conflating two different things, or possibly I wasn't clear.
Whether the kit works as advertised is not the issue - you, as the buyer, take that up with whoever sold you the stuff. Depending on middlemen, you could normally be dealing with a vendor, importer or manufacturer, but the that's between you and them.
However, as the person bringing the stuff into the country, you are the importer. Your remedy for faults is still to got to whoever sold it to you (which would be the Chinese manufacturer). However, if the kit is dangerous or forbidden (maybe it is a phone blocker, or DIY tazer or similar, or burns down next doors house when your connect it to the mains) then whoever imported that kit gets the rocket up their arse from TPTB. And as the importer that is you. Your remedy is still to go after whoever sold it to you, but TPTB@your_country won't give a toss because it's you that brought it into their jurisdiction.
In the FTDI thread does the responsibility lie with the end user or with those who sold fake chips?
Different issue complicated by end user licensing of software. The chips may or may not be fake (the only fake thing about them is the logo, and without that they would be functional equivalents that are not fakes). However, the user of the software warrants that he won't use it other then with FTDI chips, so however he got to be using the chips isn't relevant.
Let's make it simpler: Fluke and the yellow cases. The end user can't be nicked for buying or using those, and the manufacturer similarly can't be nicked for making them (unless Fluke bring an action against them in China). It's the importer that carries the can. That is, whoever is responsible for bringing them into the country, and that is Sparkfun in this case. No argument there, right?
OK, let's suppose that you get fed up of Sparkfun not supplying these yellow-cased instruments any more and decide to buy one direct from the manufacturer (presumably via Ebay). Now you are the importer and Fluke would be justified in coming after you, forcing you to destroy the kit and possibly billing you for their time in chasing you. You are on just as bad a legal footing as Sparkfun was.