Without going into details, I've been able to some some expropriation documentation and frankly...FMV is considered, and then the home owner gets ++++++. The main reason being is that it's simpler, easier, and less bad reputation for the gov't to pay people out handsomely.
Now, having said that...no home owner accepts the first offer, and we always have people yelling for more. One guy didn't like his offer, so we took it to 2 independent appraisers, and he was able to bring his own appraisal as well and we'd work off the average of the 3.
Each of the 3 came back about 100-200k LESS than what the owner was being offered...but he didn't care...he wanted 300k more than the offer.
I don't know the final bill, but they upped the offer just to shut him up...and he moved out within 2 weeks.
In addition, there is a team of lawyers that specializes in maximizing your offer from the gov't in these types of cases. The lawyers know the projects, know where the impacts are, and reach out to every home owner in the area to 'fight for their benefit' and are strictly there to maximize the amount of money they can extract from the govt.
Typically the owner gets less than just going direct with the gov't, as the lawyer takes a huge cut. But it's their business, and it is the owner's right to have their own independent legal counsel.