I think most of the scales bought at gas stations are used for drugs, but that doesn't make them automatically classified as paraphernalia as they have plenty of legitimate uses as well.
As far as how to report them on a shop, though, it depends on the brand. Some specify small digital scales are drug paraphernalia, some consider them not paraphernalia. Others don't say one way or another. For the ones that don't specify, I usually don't count them unless they are next to pipes and stuff, and in those cases it wouldn't even matter because the pipes were enough.