I went into a small bike shop near my home town to buy a shifter cable, and the guy tried to sell me some proprietary brand of cable that would have cost me $60 for a package telling me all the reasons why he was sure I didn't want to risk trying to put the wrong kind of cable into the break levers on my $300 bike...
I tried again, explaining I just needed standard break cables, he was very insistant on this proprietary model, and was sure I would destroy my bike if I didnt buy it. I rolled my eyes and left the store. I was about 210 lbs at the time, and just getting into cycling, but I knew any kind of cable should not cost me more than $5.
I have since lost weight (down to 184! in just 3 months) and I find the more in shape I get, the better reception I get from a LBS. Its a shame how judgmental people can be, especially in the cycling community.