You can be paid/coerced to vote for someone even if there's total secrecy. For example, you can take your cellphone in and take a picture of your filled out ballot to collect a payment.
Unless you want to start the confiscation of cellphones before voting in person, the risk of a coerced or bought vote will always exist.
> For example, you can take your cellphone in and take a picture of your filled out ballot to collect a payment.
And then you can go up to the election workers and tell them you have a spoiled ballot and want a new one, which they have to give you. That's one reason such schemes don't work right now.
Source: I volunteer as an election worker every year in Iowa.
In Texas, the election judges are supposed to stop you if you pull out a cellphone or any device.
Paper is all you are allowed to use during the voting process.
In-person, high-risk rule-breaking that's hard to validate has a tendency to scale differently from say, pasting a value into a lottery/payment app.
I mean, compare the number of people who've flown over Barbara Streisand's property to take a picture of her house to the number of people who had a copy of said picture in their browser cache.
You can read more about this peculiar scaling factor of the internet in Bill Gates 1995 book The Road Ahead.
You can be paid/coerced to vote for someone even if there's total secrecy. For example, you can take your cellphone in and take a picture of your filled out ballot to collect a payment.
Unless you want to start the confiscation of cellphones before voting in person, the risk of a coerced or bought vote will always exist.