You cannot "boost" your immune system (and you really wouldn't want to anyhow) - Beware of scams -
You are quite right.
Also ... my own immune system is naturally significantly stronger than much of the population, and any such "boosting" is potentially dangerous for me.
There is one upside to my immune system being as it is: my recovery times are shorter.
Fear makes you stupid. Google things before you send anybody any money!