A lot of it is.

As the other guy said you’re not actually buying data, just targeting ads really specifically. this means that you pay google to show your ad to x people and they go “okay we’ve done that” and basically you have to take them at their word.

but surely they wouldn’t lie? well, not on technicalities. for years, you could buy pre-video ads that would play on youtube, and it turns out they would also play them across various websites, not at all to do with youtube or that type of content consumption, but it’s obviously all in the TOS so you can’t sue them for bait and switch :)