probably too much cleverness over clarity but ...
``` ruby
def self.valid?(request)
  %w{ items client_number business_unit ....}.inject(true) do |valid_so_far, method_name|
    valid_so_far && send("valid_" + method_name + "?", request.send(method_name))
  end
end
```
that would require renaming/refactoring `.validate_list` to something else and renaming `.valid_list?` to `.valid_items?` so not sure if its worth it.  there's just a lot of repetition here.