Disclaimer; this is mostly off-hand knowage, might be a few details I missunderstand.

Quick edit, I'm rereading your post, and pretty sure you already know boost doesn't choose the ads, but asking to pick a different provider so..........oh well, I'm not gonna delete this.

Those adds aren't specifically chosen by Boost (or whatever site/app your using). It's whatever the ad provider decided to inject. Boost just says 'place add here' - its up to the ad provider to figure what ad to place here. The ad providers (google or facebook) use their algorithms to guess which adds your most likely to engage with, this why you'll see the same thing in multiple place, and ultimately the whole point of data collection - to sell us more shit.

If you're using Lemmy, it's probably fair to assume that you use some form of add/tracking blocker - which means the ads you get aren't targeted, and you get the ones that are paying to get broadcast randomly instead of focused based on user data (which I assume costs more, but gets a higher click through rate).

There's probably some settings the Boost developer can set up, but I'm not sure what the granularity is. Someone who has actually used the service would know, I can only assume there's some basic categories like language, age group, and generic things (music, tech, sports, ect) that determine if your site shows ads for matchbox cars or "hot (insert race&age) ladies in your area". I highly doubt there's a setting called "disable scam ads".

For a site/app to have full control of what ads they display, they would have to make deals with the actual business wanting to advertise (think a direct youtube sponser vs an auto-ad that plays whatever). For an independent ad developer that would be like giving yourself a full time marketing job, and for a business it would be a nightmare to manage every individual.

This is where the advertising agencies come in; "you pay us lots money of money and we'll find lots of "billboards" to show your ad to - give us more money and we'll only show your ad to people likely to buy your stuff"

And on the flip side "let us put a billboard here and we will pay you money everytime someone engages with it, things like popups/video/auto play = more money. We'll also buy any user data you have so we can optimize the billboards for maxium engagment, that way we can charge the businesses more to advertise and you can fund whatever you're doing (as long as it's advertsier friendly, but don't ask us for clear guidnece on that)".

Google wants to crush third party app stores/developers in the name of safety, but will gladly serve bullshit to users for as long as they get paid.