I think it's also crucial to guage what the customer doesn't want to know - some can get way too techy with non-techy customers and end up confusing them to the point where they're no longer sure that the bike they were looking at is right for them or not.
A muppet in Evans nearly talked himself out of a sale when I went along with a mate to look at budget hybrids - he just wanted something fastish and fairly comfy to ride to work and some leisure stuff at the weekend. We found a last-season Mongoose with decent parts, nice colour, right size for him, hefty amount off. He test rides it, likes it. Really all the sales guy had to do was run his card through, maybe pausing to ask if there were any other bits (lights, helmet, etc) he wanted.
Nope, he *has* to start pulling out other bikes, none of which are quite so well suited and pricier, even if they're in his budget. Then he goes on at great length about the relative merits of various parts and groupsets. By now my mate is wavering and starts second-guessing his opinion of the first, and is on the verge of walking out to think it over. In the end, after riding one of others and me talking some sense into him, he goes for the first one. Madness.
Personally, I don't take any bike shop salesperson's opinions on the quality of kit at face value and 99% of the time I just need someone to get it for me from the back and run it through the till.
