Spoke about this with my lawyer partner, and her response was there is only a legal footing if the product doesnt do what it specifically says it will do, because the advertisement is very vague and non-specific the product, doesnt have to do very much more than the stock part, with the engine operating at factory specs.
So probably no accc case, as it would be buyer beware unless the seller gave the advice that the product would perform to your specific requirements.
Sell them and get a more reputable part, perhaps dont waste your time... Seller sounds aware of theyre position