What methods can be used to determine whether they are authentic or fake?
You are getting this Elisa Kit spam from China, too? The only way I see, would be to use a known reference standard so you can titrate both the specificity and the sensitivity of the kit. Ideally you would compare it with a known and proven kit. If you have the reference available in the lab and the cheap kit is not too expensive you can give it a try. I would do it, since work time and reagents also cost money.
Just a few direct ways can figure out whether Elisa Kits are authentic or not.
Proposing to visit their factory. Generally bait company does not agree with it.
Complete range of kits. If a company has every and each ELISA Kit, it is usually fake. Unless they are very large and professional companies, such as abcam, cellsignal, sigma, sabbiotech and so on.
See the price. If prices are ridiculously low, but in the name of large companies such as import R&D raw materials packaging. This ridiculously low price can't even afford the raw materials, which company will sell at a loss?
This problem is rampant and has been plaguing the research community for a decade. I can explain how exactly do these companies make these fake kits, how to experimentally verify what I said is true, and how to spot them by just looking at their website. I can even point fingers and name a few known and notorious companies that do this malpractice. What I ask from anyone who reads this is to recognize that these companies are the bad apples in Chinese companies and you shall not generalize all Chinese biotech companies. Generalization, not a good thing, and I trust all the years of training in scientific critical thinking has taught you better :)
Now how do these companies make fake ELISA kits? Simple. They use a universally present protein target, initially TGF beta--I do not know what they have shifted to lately--to make one type of ELISA kit, and label it as anything and everything.
How to actually prove it? Run a western using a trusted third party antibody. If nothing shows up, you know the standard is not what they claim it is. Or you can also run a third party recombinant protein on the kit. Same core concept.
Do not want to bother with all that? Then just keep an eye out for this signature: one company that has thousands sometimes tens of thousands of ELISA kits, covering all kinds of species--sometimes ridiculous ones like whales, giraffes, tadpoles, sharks etc.--nothing against giraffes, they are awesome and all but seriously... These companies are literally like Noah's Ark. How can one company you never heard of come up with so many ELISA kits while established companies who have been making kits for decades are dangling on the level of hundreds or thousands?
Maybe, one thinks, that someone went hard core and just made them all, that maybe this is real? After all there are no other choices, they are the only ones selling this ELISA kit, wouldn't hurt too much to give it a try...?? And that is why these companies still exist today. That is why so many papers got pulled, and so many clinically promising indications turned out to be false. That is what cost millions of dollars of tax payers money.
At the end I want to point out that, if researchers did their due diligence, or if there are some more effective forms of media where researchers can get information like this, these companies would have died a decade ago. Instead they just keep coming up with different company names and pulling the same scam.
I want to put examples of these companies by directly referencing their names but I am not sure about the forum rules would allow it so for this post, I would not do so. The signature described above should be clear enough for you to spot these companies. Wish you all the luck in 2015.