I've had mostly the opposite experience in my bike shops. My most local LBS is a Brompton dealer so that experience doesn't count (I feel like selling Bromptons takes a bit of investment so in general they're already folder friendly). I didn't try to instigate a fight since I had my Bike Friday :-D At the next two nearby stores I always get curious looks from the employees. At one of the stores the owner/head mechanic was quite interested and chatted with me when she wasn't occupied with a guest.

I suppose that recently folders have been getting a little more common here. I just did two bike counts on our bridges this week. There were about 600 cyclists over the two bridges over a total of 4 hrs. I saw 3 Bromptons, at least 25 dahon and similar style (downtube etc.), 1 swift, 1 Montague, and a kick bike(!). (No BF, Reach, A/Strida, Carryme) That's already 5%!