I know we can't pretend to have every product tested, but if we want to have a minimum standard of quality around the DNMs it should be prevented that vendors get the same credit regardless of the real quality of their products.
In other words there will never be uncut cocaine if everyone can list their cocaine as uncut whatever that's true or not. There won't be motivation to sell quality if quality is not acknowledged.
What could be done:
a) Don't allow purity percentages / unadulteration claims on listing unless those claims are proven with an independent test.
OR, AT LEAST
b) Ban/punish vendors who have commited fake advertising after they are proven wrong.
OR
c) Modify the listings that contain blatantly wrong information and prevent those vendors from publishing this kind of information in the future.
How, exactly, do you propose that be done? Even just monitoring product listings closely enough to identify every time a vendor makes an objective claim about purity/quality that could be tested on any of the more active markets would take a lot of manpower, probably more than the existing admin teams could reasonably do without bringing in a lot more people. Bringing in new people to a darknet operation is hard - you have to somehow determine that you can trust those people in a community where we all take active steps to make it as difficult as possible to determine our real identities or anything identifying about us as individuals. Even if they don't have any backend access to parts of the market that could potentially be used to pull off a scam of some sort, you still have to worry about vendors getting themselves or their paid shills in on that team and corrupting the results.
And that's just to flag claims that this policy should be applied to. What then? You can't just ask each vendor to provide one small sample to a tester (or worse yet, just provide what they claim to be authentic test results from a third party), since they could just send one sample of much better shit than the product they actually send out to the rest of us. You could have the admins randomly place small orders with these vendors to do 'secret shopper' type testing, but that would be a constant flow of money out of their pockets and it could have the unintended effect of encouraging scammers since they can expect to get at least 1 or 2 of these 'testing' orders for their scam listings. Even legit vendors would start including quality claims even where there's no real need to do so, just to get a couple extra free sales out of the testing process.
Even if you can somehow work out a system that reliably gets representative samples of the goods being sold and apportions the cost of this process in a reasonable way, you still have the problem of actually testing the sample. Constantly mailing in test samples to labs for GC/MS and the like seems like a pretty big opsec risk. I certainly wouldn't volunteer to be the one constantly receiving small orders of hard drugs from questionable vendors and constantly shopping small samples of hard drugs out to major drug testing labs. But without sending a sample to a reputable lab that offers this sort of service, there's no practical way to evaluate the accuracy of things like cocaine purity claims, to categorically rule out the presence of specific cuts, etc. Some claims, like LSD doses per hit of blotter, are virtually impossible to verify with much precision.
And then there's subjective aspects to whether a claim should be called out as wrong or not. For example, it's pretty widely accepted that there is little to no truly "uncut" cocaine anywhere outside the main producing countries, since the cartels take the pure product straight to adulterant labs that add the first round of cuts to each batch before it's ready for export. If someone claims to have 'pure uncut Colombian coke', and it tests out to have a small amount of impurity consistent with the best product known to come from Colombia, is that claim false (because it's not actually that mythical stuff known as truly "pure"cocaine), or is it true (because it is the purest grade of Colombian coke that anyone outside the cartels will ever likely get their hands on)? What if a vendor consistently lists their MDMA as 84% pure by volume (The highest possible for the most common salt form), but one batch tests in at 83.8% Is that worth labeling as 'false'?
It would be great if we could have perfectly reliable info about the exact quality and chemical composition of the illegal drugs we want to buy. Sadly, that's just not how black markets work. This is what happens when you don't have access to basic rule of law institutions that can effectively enforce rules against fraud.