I have never experienced anything but welcoming attitude by any shop in which I spend money. I really don't think they have any idea or concern about what I do outside their shop. In other words - they have no idea or concern that I do my own repairs and sometimes buy stuff at other shops or online.

I suspect you're being paranoid or happen to go to a shop full of jerks (in which case, why would you ever go back?)

Now, none of this is to say that some shops don't have fairly ignorant sales people, but I've never gotten a negative attitude, just good natured ignorance, but happiness to sell me whatever I wanted to buy from them.