As I say there are third party certified supplements. There are good supplement choices and bad supplement choices and penalties accordingly.
USADA take into account degree of risk.
At one end, you have a fighter that only uses third party certified supplements, that thoroughly researches brands etc before using them. They are deemed to have taken little or no risk, and will probably get nothing more than a warning.
Then you have an athlete who doesnt use third party certified supplements or do thorough research, but buys what they think are reputable looking brands. They will be deemed to have taken a certain amount of risk. They maybe get 6 months for their degree of fault/responsibility.
Then you get an athlete who takes no care at all, buys supplements called Super-Shred-Gains, from no name websites.. they have taken a much higher degree of risk and must bear a greater amount of responsibility.
Then you get the guy who has taken a dick pill, which was crushed and broken,l from a packet that said "for research purposes only - not for human consumption", they are deemed by an arbitration panel as "reckless"