Most international firms have an "unsubscribe" button on their marketing emails and it (usually) works. HK firms appear not to and it seems to be impossible to stop them sending you crap. I find the real estate agents the worst (so I rang up and yelled at them) and that seemed to work eventually. But shops too - and it's really irritating.
Anyone else got any good ideas for how to get off these mailing lists? (Pricerite was the one that prompted this post, for example.)