This raises two economic issues.
One concerns the fragility of social norms. Why did Ms Thompson break the norm of her profession? One possibility is that she doesn’t consider herself a professional; she did not charge footballers who didn’t look like Shrek for her favours. Another possibility lies in the abundance effect; proximity to wealth makes people behave worse. And a third possibility arises from peer effects. Ms Thompson’s peer group seems to be good-time girls rather than professional ones, so she was not sufficiently exposed to prostitutes’ moral code.
A second issue concerns contract enforceability. Mr Rooney probably thought that, in handing over so much cash, he was buying silence; such is the demand for sex with footballers that even he could get it for free. Ms Thompson broke this implicit contract.
But this contract was unenforceable - and it would have been, even if prostitution were entirely legal. Ordinarily, there are three ways of enforcing a contract. One is the threat of violence. But Mr Rooney couldn’t have used this, as it would only have made a better story. Another is to sue. But Ms Thompson doesn’t have the millions that would compensate Mr Rooney, should he get divorced. The third possibility is to rely upon the seller fearing a loss of reputation. But Ms Thompson probably judged that the gain from selling her story outweighed this cost.
Put together, these issues imply that there is a potential market for lemons problem between famous men and prostitutes. Fearing that prostitutes might sell their stories, men will tend - at the margin - to avoid them. This will reduce demand even for good prostitutes, who in turn might withdraw from prostitution into near-substitute professions such as acting, modelling or PR. The upshot will be a sub-optimally thin market. In this sense, Ms Thompson's behaviour has potentially serious consequences.