Mostly true but sometimes you can sell on a secondary market or through a tender offer.

At least for one of my previous employers, the secondary market was not interested. I personally wouldn't count on it unless one is working for a highly visible startup ;)

Definitely true, and many times there are clauses preventing you from selling to a 3rd party before IPO anyway.

Usually those providers don't "buy" it from you.

They do fun things like giving you a loan with the options as a collateral. You would then default on the loan at the point of IPO.

So theoretically you don't sell them anything.

Interesting, I had never heard of that.