WIY, with all due respect, I say good Shabbos to everyone I see. If I were to see 50 people, I would say GS 50 times. There is no reason not to say GS to someone. It is not flirting, it is not improper, and if people think it is pritzus, in my humble opinion they have no idea what pritzus (immorality) means.
And btw, please name the accepted source that asserts that “hevei makdim” refers only to someone to whom you should be speaking. I am curious to know this.