And sure, Thork is right in that parties lie in them. So people would have to take that in to account when they choose to vote.
So what is the point in reading the manifesto if it can be full of lies?
There are plenty of people who think a big bus lied to them in the Brexit referendum. Many think the government lied to them about the dangers of Brexit with wild doom predictions and even plagues of super gonerea. We are 5 years later and still no one really knows who told the truth, how it really effects them and whether the opposite outcome would have been better.
So "I don't like foreigners" was every bit as valid as "Brexit will save the NHS £350m a week". The manifesto pledges don't mean anything. Testing people's ability to remember who told what lies isn't helpful.
But ... absolutely everyone should be able to look at the current incumbent and think "I want that fucker out". And you don't need to know the manifestos to have such an opinion because their governance is your lived experience. And if you hope for something better, vote for it.