É verdade.

Feminine charm is a measurable phenomenon, scientists have established, with women who employ it enjoying the most success in negotiations. 

Results from the first academic study of the technique shows that it can increase success rates in negotiations with both men and women by as much as a third.

Effective feminine charm combines flirtation with friendliness and women who get it right can get around 20 per cent off the price of a car, according to the study. (...)

Researchers believe the evolutionary roots of the technique lie in the Catch-22 situation women face in many day-to-day negotiations. In order to succeed in a male-dominated world they have to adopt a masculine style, which is not liked. But failure to do so makes them appear less competent. Feminine charm allows women to mitigate the antipathy aroused by their male-like behaviour when negotiating.

Fonte: The Independent

Tenho várias provas disto. Pessoais e não só e funciona em muitas as áreas para além do mundo profissional / empresarial. No entanto, a questão é esta: já experimentarm verificar se os homens que usam "charme masculino" têm mais sucesso do que os outros? Desconfio que a resposta seria um rotundo sim.
Dois exemplos clássicos de como o charme é sempre uma arma eficaz para quem o sabe usar: