Is it permissible in Sharia for an employee, by virtue of the nature of his work which precedes the implementation of a project in Makkah, to purchase lands whose locations are unknown to the general public, for the purpose of financial compensation when properties are expropriated or for commercial benefit, and is this considered a trick or a deception?

The purchase is valid, but your landowner has a right over you to be advised, as the Prophet, peace and blessings be upon him, said: "Religion is advice." So, you must guide him to what benefits him in this world and theathereafter, teach him what he is ignorant of regarding his religion, help him with words and deeds, and love for him what you love for yourself of good.