Hi Normski,
It happens unfortunately. It did for me with a '13 F30 BMW 330d M Sport. Lovely car, all the bells and whistles, hugely expensive, went like the clappers, looked absolutely fantastic, could absolutely take it or leave it. So it went back and it cost me a fortune.
The other side of this is that some cars you don't expect anything from totally take you by surprise. I bought an '03 Volvo V70 2.4 Waft-o-Matic that the guy selling described as "a good 10 yard car" and loved it so much I bought another one. Absolutely battered, well over 100k miles and just drove it at every opportunity.
Just one of those things.