A man needs his bike fixed. He will not say what's wrong with it, nor what he's 
hearing or feeling. Only that it's broken. Fix it. He's doing this to challenge 
me. No matter what I find, it's not the "broken" he's thinking of. No matter 
what I fix, it isn't good enough. In an extreme case, he may lead me down the 
wrong path (ie I find that his brakes are sub-par and fix those. Maybe he'll 
even tell me that they're the only problem. But what originally caused him to 
come in is a loose headset). If I miss something that breaks further, he will 
blame not only me doing my job, but my gender. This reinforces his negative 
stereotype of women in non-traditional roles. But is it my fault? No. He set me 
up to fail by not telling me the problem. And he would do it to any woman 
sharing my occupation. Again, an ideologue and the problem is neither me nor my 
chest. It's him setting me up to be the problem. But word will get out that xx 
shop has a bad mechanic just the same.  

If you Have an REI near by ask for all of  the check off list they have for Basic tunes, to Overhauls. I have found when I work from a list and add to the list that I do not miss little details of a repair. If every guy did this to you I would call it sexism. Sadly as a guy in a bike shop I meet men like this all the time, We do not call them sexist bastards, we just call them Dicks. Step back and look at the issue, Was your work at fault, if so upgrade your technique. ( all of us can learn more) Is the customer way too picky. Then he is a dick, if he says that the work is bad because you are female then he is a dick and a sexist bastard. Refer him to a really crapy mechanic.
I meet anal picky customers all the time. I am older, I do not take guff form them. I tell them what they asked for, and what I gave them. I always give more than they ask for.
Example of what I do on a brake job:
I clean every bike from head to tail, I clean each rim in the sink with Dawn and a Scotch bright green sponge to remove metal oxide and oil , I sand each brake pad to remove the metal oxide. I round, dish, tension, and true the wheels. This is all the extra set up I do to prepare brakes.  Then I do all the normal brake pad alignment, and toe. Check cables/ housing, caliper / lever mount bolts. Customers never come back to me with squeeky brakes when I am done. Thus lots of bad feelings are avoided and lots of rework is avoided. Sadly I never hear any good coments from customers, But I do not hear negitive ones either.
I can do all this because I practice being efficent, thorough, and Fast. As you become more experienced challenge yourself to do things better with more detail and faster. Never compromise safety. The safety of your hands or your customers life.