What gives Gautrain the right to expropriate private property?  In ancient times land was granted or taken away by chiefs and kings, often violently. This hitting-over-the-head quality flows into the modern US term of "eminent domain", the power of a national or local government over all land. But is it fair?

It depends on which country you're in. Section 25 (3) of the SA constitution requires government to pay "just and equitable compensation". In practice that means market value. It can expropriate only for "public purpose or in the public interest". Expropriation procedures are laid down by the Expropriation Act, 63 of 1975.  How can I be sure to get the right price in an expropriation?

The minute you receive an expropriation notice, your property is expropriated and you have no further recourse. But you can hire a lawyer and valuer and argue in court for a better price if you think government is paying you too little.

Is there no way I can stop an expropriation? Only if the expropriation procedures are not followed properly. One Gautrain expropriation has been tested in court on that basis, though the effort was probably calculated to get a higher price in return for dropping the proceedings. It failed.