They're running a business, not a charity. Being polite and respectful is a given anyway (it's not like you should only be polite or respectful when you want something, right?) and I've seen SAs tell obnoxious customers who've spent a bomb "sorry no birkin"... This is a case where unfortunately demand far outstrips supply for a certain good. I don't think it's unfair for birkins to be allocated to customers who've spent more...