Interesting thread. Saw an Alexander McQueen shirt in a charity shop in Islington, north London, for £18 last week.
I was about to purchase it when I realised that I was only doing so because it was AMcQ; quality wise it was no better than a high-street shirt and the colour was a rather foul mocha! Before you say it, no it wasn't fake, it was certainly real, just thoroughly unremarkable.
I have made mistakes in the past of buying things in charity shops purely because of the brand and then regretting it two weeks later.