They're absolutely crap in there. I had a row with one of them who insisted there was no such thing as a Cat 5 crossover cable and that you couldn't connect two PCs without a hub. In the end some young guy working in the upgrade area told me that they had to stop stocking them because the staff kept getting them mixed up with regular networking cables.
(The look on the managers face was priceless, being corrected by some snot nose teenager!)
Dexter