For cars, I walk if I don't like the salesman - after being very polite and finding out when s/he's working. I then come back at a time other than that and get another. :) It's rare to need more than two before finding one that's willing to work with me (take my offer or not - no negotiating).
All three of my trailers were bought from RV Wholesalers through email. I never talked to the sales person until I showed up at the store to take delivery. (Usually have to call and talk to the finance person though, but they're all business.) Wouldn't mind buying cars that way too but haven't yet found a local dealership that does it, and I've tried.