That's why there is voting secrecy. You can pay someone 20 euros but they vote someone else.
That is done for good reason, you can't waive it away with 'voting secrecy'.
'voting secrecy' can be defeated pretty quickly by asking the voter to take a picture with phone and report it.
you have a phone and the voting booth is private, how is anyone going to catch you?
the other old school (90s) way was you were given an already stamped paper and you had to return an unstamped one to get the money.
or if you want to go communist old school, you had people looking at you through holes in ceiling.
After all, if they are endorsed by the Party, why do you think you can do a better job, citizen?