Drug cryptomarkets may increase information available to market actors, which should reduce information asymmetry and increase market efficiency. This study aims to determine whether cryptomarket listings accurately represent the advertised substance, weight/number and purity, and whether there are differences in products purchased from the same listing multiple times. A 2016-17 dataset of law enforcement purchases from cryptomarket vendors (n=38) was matched with a dataset of cryptomarket listings (n=23). Almost all (92%) samples contained the advertised substance (mainly cocaine, methamphetamine, MDMA and heroin). In most of these cases (85%) drugs were either supplied as advertised weight/number or over-weight/number. All six listings that quantified purity over-estimated the actual purity, which varied from 11% to 58% less than advertised. There was no consistent relationship between advertised purity terms and actual purity (e.g., “free base pure cocaine” was 95% cocaine, whereas “purest cocaine available. pure uncut” was 58-66% cocaine). Across the six listings purchased from multiple times, repeat purchases from the same listing varied in purity, sometimes drastically (e.g., 18% vs 73% heroin), and while this was to be expected with long gaps between purchases, wide variation was also detected on listings purchased from only one month apart. In conclusion, cryptomarket listings are mostly accurate, but the system is far from perfect, with purity typically over-estimated. Community-led attempts at market self-regulation have been reported and warrant further investigation with more current data including a larger and less biased sample.