I can see how that would be a concern, and I'd say to that - it really depends on the implementation.

You could have a blockchain-based system where everything is public (say, like Bitcoin), which from your perspective would be bad.

You could have a blockchain-based system where you need a "view key" in order to actually view the details of a particular transaction (say, like Monero), which from your perspective would also be bad.

In the latter system I'm describing, you could have a procedural control that you have a choice of receiving your "view key" or something along those lines to deter coercion and vote buying.

Other possibilities would be allowing voters to change their votes at a later date, or creating a system that allows voters to vote remotely such that they could do so in the comfort of their own home where they'd be (presumably) free from coercion and other influences.