You make a valid point indeed.
My concern would be more that it says its one substance, but in reality may or may not be contaminated or replaced with others. For example, the counterfeit product that my wife purchased on Amazon was a personal humidifier, which is a unit that vaporizes water to help hydrate the nasal passages and throat (she’s a singer, so it helps when changing between climates for singing gigs, after getting dried out due to air travel, etc.). It comes with packets of liquid to be used in the unit, and breathed in by the user.
Luckily, the fake product broke quickly, and we realized it was a counterfeit after contacting the company directly, and them helping us get a legitimate unit. However, we still have no idea what was in the first few packets that my wife vaporized and breathed into her lungs through the counterfeit unit. My concerns would be the same with buying “fake” fructose/glucose from a non-reputable seller.
However, I think everyone else has given some good suggestions, above.