On occasion I need to compose a business letter in Spanish. Usually I am doing this with help from Dominican friends. They often have me writing some pretty bad Spanish--sentences without verbs, runon sentences, etc., and I'm able to catch those mistakes. But it seems like they always start out with Por este medio nos dirigimos a Ud., and end with Sin mas nada. To me it sounds like a nine year old's writing, but I realize that may be me thinking in English. Are these appropriate or not?