Sorry, this is a weird post as it isn't a question, it's hopefully for a lady I met (as the title says) in the lingerie changing room in Debenhams today and I'm sorry again because it will go on a bit while I explain!
She was there with a younger lady (probably her daughter), who was having a fitting because she had stretch marks I think. I apologise for listening to the conversation, but it's difficult not to in those changing rooms and after reading all these bra intervention threads, funnily enough you just can't help it! 
I didn't see the young lady in question apart from when she was accidentally reflected in the mirror I was looking in, and obviously I looked away immediately, but the glimpse I got suggested a fairly slim lady with large breasts - much, much larger than my own 30Gs.
The assistant had measured and was helping find bras and apart from what I suspect was a bad starting point because of her training, she was doing a good job - she immediately went down a band size when she discovered that the young lady had done the bra up on the tightest hook, and explained that a new bra should always be wearable on the loosest hook. She explained about issues with t-shirt style/moulded bras and suggested the young lady looked more at balcony styles given the shapes of her breasts, one breast usually smaller than the other etc etc - all good stuff 
She knew her stock too.
However the assistant started with a band size of 36". As I said, I didn't really see the young lady, but her mum was a slim build and I doubt the 36". They progressed to a 34" but the young lady still did that up initially on the middle hook because she she couldn't see and that was the hook that felt better. I don't think I heard anything larger than an E cup being mentioned, though maybe there was an F. In the balcony styles the young lady didn't seem to feel supported - for obvious reasons!!!
I wanted to say something, but it's so hard when the assistant is there and trying her best within the limits of her training (and bear in mind that I may be wrong about all of this as I didn't actually see any of the bras on, so I could be doing the assistant an injustice). In the end I whispered to the mum to google 'mumsnet bra intervention ' and have a read (on the basis that she had mentioned she should probably have a remeasure too). I think the assistant heard though and wasn't happy, which wasn't my intention as in many respects I think she was good. Perhaps though, she will goggle it too and read this, and if she's as keen to get it right as I think she was, will decide to check out some of the other bra interventions threads and read the 'miracles'.
So if anyone from today is reading this ... I bought a 30G (to the huge surprise of the assistant who helped me look for another one!). If you're the young lady's mum, you saw me dressed in a close fitting jumper and I think you'll agree that your daughter is larger than me. If I'm right and the final bra was a 34E/F, then the young lady was wearing a bra that was much the same size as mine, relatively speaking. The lady being fitted looked so much larger than me in the glimpse that I got, that I doubt she fitted into any of Debenhams stuff at all - my guess is we're talking 32L or something. So please try Bravissimo in Reading, ladies (opposite the side door of John Lewis). And read as many bra intervention threads as you can until you're convinced
To the young lady concerned, I sincerely hope you find the right bra that will support your fantastic breasts and stop you getting any more stretch marks. Good luck! And I do hope nobody today from today is offended by this post - that isn't my intention and if you are then obviously I will remove it.
Apologies for having bored everyone else to tears!!! 