I think it's all about money, claudias lifestyle seemed to greatly outstrip her income, I think her liking for middle aged men was for financial reasons, young men have mortgages and children to pay for, a middle aged man, married or not probably wouldn't believe his luck if a much younger and attractive woman like claudia made a play for him and would I think be quite happy to keep her sweet financially, maybe she got a bit greedy, or threatened to tell his wife or girlfriend and he decided he had too much to lose and killed her, or possibly, drugs have been mentioned, maybe she got a bit careless after a drinking session, saying things she shouldn't have, maybe she wanted more money, or possibly someone thought she might implicate them