I wouldn't trust anything on the street. It's not a question of absolutely safe/absolutely not safe. If I had to bet money on which is statistically more likely to be safer, I would bet on what comes from a licensed pharmacist directly into my hands vs. buying something from a person on the street.

It's a big gamble. It always has been and always will be. Black markets are driven by expediency and profit, full stop. Safety does not enter into it for black market businesses.