while i'm not a lawyer or working in the supplement industry
but if you are a reseller (just reselling other brands) i don't think you would have to worry too much about public liability insurance, i mean how could you be held accountable for the actions of others , how could you be liable because the brand you are selling screwed up
if you were selling your own branded stuff things might be different , but if you are a stockist/reseller i wouldn't worry too much about it
this is not legal advice ,