eBAY, Gumtree, and Autotrader are NOT scam sites.
While you're at it, don't forget all the other classified ad sites, the small local classified ads newspapers,and every dating and social networking site on the internet. And don't forget the "real" newspapers, radio stations, and TV stations that allow commercials and "infomercials" for useless items, bogus weight loss products, and an entire industry of anti-aging products that don't work. And let us not forget sites like Amazon, who allow these scam products to be sold. By logical extension of your theory, they are all fraudulent.
I have stated before that this is not the site for posting blanket accusations of criminal activity against legitimate companies.
Those companies provide a service. They clearly specify what that service is, and they also make it a point to warn people of the risks. There are CLEAR warnings on their sites.
They are also not involved in any financial transactions with you, nor are they likely to be found responsible for your financial interests in any court of law. Unlike some of the money transfer/exchange companies that get a piece out of every transaction, these companies also don't profit directly from the scams. If you (or anyone else) sends money to a scammer by WU, MG, or bank transfer, none of those companies profits. More often than not, they end up absorbing the cost of the fraudulent ads.
These sites are under no obligation to remove an ad just because someone emailed a complaint about it. From the site's perspective, the fact that you (or anyone) reported an ad as fraudulent doesn't guarantee it is. You could just as easily be an angry person trying to get back at an ex, a scammer reporting an ad because you are angry that the victim didn't fall for your lies, a confused individual who really believes a legitimate ad is a scam, or even someone angry because the seller didn't accept your offer. All of the above happen regularly.
And how do you think the legitimate sellers would react if their ads were removed based on a bogus report? They too have bills to pay and businesses to run. They will also lose money if their ads are indiscriminately removed based on unverified reports.
These sites have every right to investigate before taking action. If they don't know the person making the report, or the information is incomplete, the ad may not be immediately removed. As long as they are following an appropriate process, they are not going to be charged with any crime. If you want them to respond to your reports sooner, then you need to make the effort to understand what needs to be done to make that happen--I can guarantee that accusing the site of fraud is not going to elicit a cooperative attitude from them.
As an individual, if you are not happy with their actions, or feel that you are at risk, you have every right to refuse to use their sites. You also have the right to start up another site that has whatever controls you feel are necessary.
We see accounts used for fraud in many countries, not just UK.
David asked for the contents of the messages for two reasons:
1) scammers often use the same words over and over again. Posting the actual language can help many more victims to recognize the scams when the criminal changes names and/or phony info.
2) It also provides objective evidence that the account really is linked to scam. As I said above--false reports do happen. Banks can't just take action against potentially innocent parties with no evidence to support that their activities are truly fraudulent. Posting the text from the scammers helps to ensure that they (and we) are going after the right people.