On Facebook? It's ads for products where they do a bait and switch or claim to have some kind of "difficulty" and never ship a product or ship some garbage instead.

Example: My wife saw an ad for decorative skulls that were made in such a way that you can safely put them in a campfire for Halloween. They had a video and everything, it looked pretty good. She orders a set and they get delayed, then she gets and email saying that US Customs would not let them in the country and they instead ship a $0.50 plastic Christmas tree ornament instead and immediately ghost her.

We reported the company to Facebook but it continued to run for weeks. I've also seen ads for $500 Aventon E-bike "closeout" that's clearly a scam, reported it, and had no action from Facebook. Another ad for an all metal "puzzle kit" of a V8 engine listed for $50 that I guarantee is fake. Every day I get ads that would not have passed the smell test from any reviewer yet continue to run.