As a previous seller of outdoor and climbing equipment i would say a good sales assistant will depend on the customer, some people know what they want and only require you to complete the transaction, those with less experiance will require you advice and opinion, it is your job therefore, to understand what they NEED and what they WANT using your experiance, a sound knowledge of and actually doing the sport is crucuial.An understanding of the weights of every bottom bracket, headset etc is not . The 3rd and possibly most crucial aspect is the ability to make a good cuppa , eat excessive amounts of cake and stare out of windows while bored out of your brain.