Too many voters
Watch the turnout figures ‒ they can be a big giveaway.
You never get a 98% or 99% turnout in an honest election. You just don't.
Voting is compulsory in Gabon, but it is not enforced; even in Australia where it is enforced, where you can vote by post or online and can be fined for not voting, turnout only reaches 90-95%.
The main reason that a full turnout is practically impossible is that electoral registers, even if they are recently compiled, can rarely be 100% up-to-date.
