Coupons allow instructors to promote their Udemy courses to students on and off the platform. Coupons are allowed only in promotional announcements and the Bonus Lecture. They cannot be used anywhere else on the Udemy platform, because once students enter a course, they expect a safe learning environment where they will not be “sold” to.
I cannot make sense whether in the above paragraph the learning environment is being sold to students or students are being sold to someone/somewhere.
There is a to which you are overlooking.
....where they will not be sold to...
Compare:
I do not like to be spoken to in that manner.
To speak to someone. To sell to someone.
A product can be sold. (marketed)
A consumer can be sold. (convinced to purchase something)
A consumer can be sold to. (subjected to a sales "pitch")
There is no paved road to the dig site. It must be hiked to.
The child was cranky and wanted to be sung to.
This is a class of verbs taking indirect objects. I do not "speak you", rather I speak to you. The mother does not "sing her baby", rather she sings to her baby. We do not "drive the stadium" we drive to the stadium. A person does not "sit a chair" but sits on a chair.
A chair is for sitting on. A chair is made to be sat on.
A house is for living in. It is designed to be lived in.
The sliding-board in the playground is for sliding down. It is designed to be slid down.
The coconut tree can be shimmied up.
A narrow passageway in a cave can be squeezed through.
....where they will not be sold to... is thus the passive form of "where (we) will not sell to them", i.e. where we will not subject them to a sales pitch.
