No it’s true that anything can be poisoned even your beer leaving it on a table. Usally your supplier and the people in the culture will know what is good and where to get it... it’s only a concern I would have getting stuff from random people.
This is all very poor advice.
Get chemical test kits, use drug testing services where they are available, be cautious.
Which is pretty terrible itself, powders and crystals can be just as adulterated as pills. Relying on sight and taste to tell what you've got is very unreliable.