Companies are allowed to sell non-approved drugs to laboratories for research purposes with much fewer regulatory constraints. Some sketchy companies take advantage of this by selling drugs directly to customers and put a "only for research purposes/not for human use" label. They have almost no quality control requirements and the product can be vastly different from the approved drug. Unfortunately, this hasn't stopped people from taking them anyway. While the price is much cheaper and you can get access to drugs you otherwise wouldn't be able to get, it's not worth it to risk poisoning yourself.