I know that feel. Used to work in electrical retail, (selling TVs, Hi-Fi and the like.) Amount of times you'd spend a solid half-hour or more going through LCD/LED/Plasma, HD-Ready or 1080p, what brand, what extras, etc, etc with a customer to set them up with the right stuff to suit their needs, and they go, "anyway thanks for your help, but the prices are a bit steep here so I'll grab it online."
I may be biased, but it felt damn rude every time.
The worst ones were people at the local store who would play games there, buy stuff online, then come down and boast about it and how much cheaper it was. :/