I don't know what various countries' norms are, but if people aren't used to political ads and are generally suspicious of the concept, an ad may have negative utility.

I know if I saw a paid ad for a candidate that would make me want to vote against them.

Not sure about the EU-27, but the UK has rules about election ads, to the extent that Cambridge Analytica was a scandal. Some of that scandal was due to bribery and offering prostitutes, but even the aspects that were purely what is considered "normal" for targeting online advertising was unacceptable by UK political standards.

That said, part of the latter being scandalous assumes that they were actually capable of providing the service they claimed, which is something I find myself increasingly unable to believe due to how wildly badly I get categorised by the main advertising platforms — nationality, country of residence, language, gender, all wrong.