While some job sectors have implemented open pay scales, and there is a degree of legal recourse for anyone who can provide outstanding evidence of discrimination, countless instances of unfair pay occur in a more insidious way, entrenched in cultural attitudes and the good old capitalist urge to find any reason to pay employees as little as possible.
As an amusing tale (although I wasn't laughing at the time) is that I once worked in a place where a family man was having trouble at home - through no fault of his own - but it meant he was away from the workplace for months on end, and I had to take over his role as well as carry on with my own.
When he came back, he was given a pay rise, while I got nothing. When I went to make my case, I remember being told that if I wanted more money, I should cut back on 'going out'. Given that I was a focused individual who was working a lot of overtime in that office, evenings and weekends, and had a alcohol-free lifestyle, for someone to imply that, if I was given the money, I'd fritter it all away on stilettos and a bar tab, was the most misguided statement that man ever made.
That company knew how hard-working I was, but they thought I would accept whatever they said, they were relying on me to just roll over and get back to the job.
After I left, there was a girl who got a decent pay rise, through doing something else other than work, and that ended with her getting the sack not long afterwards, when the novelty wore off and she became an inconvenience - so in that case, sex appeal led to an even bigger dead end than a future of merely being continuously underpaid for your efforts.