If we're being pedantic, then I'd say "old stud finders" are still being sold (second hand for example), so "every stud finder for sale these days" isn't correc

If we're being pedantic, then I'd say "old stud finders" are still being sold (second hand for example), so "every stud finder for sale these days" isn't correct either. Best to just say "most" or "some" to cover all corner cases :)