If you’ve never encountered the ubiquitous “listings with variations”, it is a little surprising; they are plentiful on eBay.

Strictly speaking, the way in which they are used by many sellers (in particular Chinese eBay sellers) is not the way in which they are intended to be used as per eBay policy. It’s supposed to be for listing an item where there are various options such as colour, size, etc. It was not intended as a way for sellers to throw vaguely connected items (including one very cheap one as a “lure”) into a single listing.

Of course, you can try to report them. You’ll be knocking yourself out to no good purpose, though, as eBay Australia haven’t the authority to crack the whip over Chinese eBay sellers, and eBay.cn certainly won’t take down such listings or sanction these sellers, not even with a whimsical declaration that they’re not the Messiah, they’re a very naughty boy. I’m not asserting that anything which any Chinese eBay seller does is regarded with impunity – but it’s not far off that situation.

I suggest that you avoid listings where there’s an unrealistically low price for an item, and definitely avoid listings where there is a price variation. 

For your consideration 

And… yes, as has been said, you cannot trust that you’ll get a genuinely compliant smoke detector that is truly of the required Australian Standard from someone who’s either in China sending the cheapest garbage made of the cheapest and utterly insufficient components, or is in Australia dropshipping or importing those same garbage items. Penalties apply to having noncompliant smoke alarms, quite apart from the risks involved in installing cheap dangerous electrical items.