I've always hated advertising, but I hated it even more once I worked in advertising.
That being said, it's unfair to advertisers. (ugh, I hate saying that, because it's a slimy business, but this is the reality) Nobody has the time to thoroughly research EVERY business that wants to buy advertising. Also, there's a fine line between scams and completely legal yet manipulative business.
Bill might be starting a legitimate small business and wants to advertise to get his first clients. There's very little information available online and no reviews because he's just starting out, but that could look like a fly by night scammer.
Joe owns a similar small business. He charges too much and he doesn't do very good work. That's not illegal, but people who use his services might feel like they got scammed.
Bob's a piece of shit. He wants to take your money and give you nothing in return. He knows what an advertiser would look for to verify his legitimacy, and he makes a fake website full of fake reviews.
In this instance, the advertiser might refuse to sell to Bill, get sued for selling to Joe and spend money and time proving that he's technically legit, and perhaps not even know that Bob's a scammer until months after he's taken the money and run.