Based on a comment further up, my understanding is people buying on the secondary markets are not actually buying the shares. They're just offering $X to an employee now in return for being entitled to the full sale price of that employee's shares ($Y) immediately after IPO. $Y could be higher or lower than $X (that's the agents risk) but at no time does the agent actually own the shares.
People buying on secondary markets often directly buy shares. They only resort to derivatives when they're unable to buy directly due to stock restrictions.
Yes, but the type of restriction matters. Sometimes it's just a ROFR at the same price, and that alone isn't enough to deter either buyers or sellers from directly buying and selling.
