There are many articles on websites telling you how your perfect bra should fit, and many "professional fitters" attempting to relay that information to the customer. Any fitter will know that you need to fit to the body of the woman not just the shape, and usually with brands today there is no need to add four or five inches (if they use the tape measure to measure you) to the underband measurement. But rarely does the fitter ever ask the two vital questions which would eradicate the countless items of bras you try on.
1. Are you unhappy with the current bra you're wearing, if so what?
2. What are you looking for in a bra?
By asking these two simple question - you can glean more information than trying to sell a bra to her just because you think it fits right. For example I use to work with a girl who wore a 36B, if I had fitted her I would have firmly steered her into a 32D, as I demonstrated on her that I shouldn't be able to grab the back of the bra and pull it out quite as far as I could. But her reply was, she never wanted to feel the bra on, she felt supported enough, she never fiddled with her bra during the day and liked the way her clothes fit with that size. So who was right? Now there may be fitters all over the world gasp at this - but the answer is her.
In answer to the first question, she wasn't unhappy with her current bra, and what she looked for in a bra was the same fit and comfort she gained from the bras she owned. If the answer to the first question was she needed more support, then she would have to move down a band size and up a cup size.
Bras should be about comfort and support, but most of all when wearing them they shouldn't feel like a torture device. A good fitter can lead you only so far, it they don't ask you those two questions, speak up, especially if you spend the day adjusting your bra, don't buy lingerie that will sit in the bottom of your drawer, because beautiful bras are made to be worn.