Do you think that sites and stations should be liable for advertising fake and fraudulent businesses?

I think they should be pro-active, verifying advertisers before publishing, and publishing only the genuine ones. Not do as they do now, react to wrongful material only after its publication.

Verification:

Genuine, physical trading address - which might a private home.

Named proprietor / director(s).

Proof of trading (though with some safeguards for a bona-fide new company still looking for its first sales).

Registration where applicable with a recognised trade or governmental body. (In the UK that may include Companies House, HM Revenue & Customs; the Financial Conduct Authority for money-trading; or various technical assurance-schemes for certain building trades.)

Electronic addresses (web-site and e-post) and telephone numbers traced to source; that source scrutinised for its reality. Failure will mean automatic blocking.

Nature of the advertisement's contents: "legal, decent and honest" or making spurious promises like "guaranteed" financial returns or supposed health benefits? For financial services, any statutory warnings to potential customers, such as of the risk of investment values falling or property being repossessed.

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- These conditions to be posted openly on the site, ,with a very clear warning that advertisements not meeting them will be rejected, and suspect background information may be passed to the appropriate authorities, including the Police.

I think sites should do some sort of reasonable due diligence to check the credentials of the advertiser. We need legislation to make the requirements clear.
It would be easier enough to write and update surveillance software, and have a team of humans checking the ones that get flagged due to key words or phrases, like "guaranteed wealth".

Maybe the advertiser should be required to get a police record check with a number; then site or station uses the number to verify with the police - or something like that.

But scammers get increasingly sophisticated. As soon as they're caught, or suspect someone's onto them, they shift identities and details.
I doubt that any site could keep up with the vast array of types of scam.

Ultimately the responsibility for crime is on the criminal.

And we ourselves have to be vigilant. Avoid anything even the tiniest bit odd and report it.

Yes. 100%

Of people are getting conned because you helped them, that’s being an accessory to a crime..

They are advertising platforms, not business raters. Buyer beware!

Maybe if they got slapped with a fine or something they'd actually moderate their ads