I never have any issues with not getting the spring onions for free - I grow my own veges.
I have been here 3 years, speak a few phrases, and routinely get laughed at for my pronounciation. No need to learn the local lingo, english is an official language. As Missokstic points out, the locals are far more likely to laugh, rather than marvel at your linguistic skills and give you a whooping discount :
the four most common reactions to a foreigner speaking Cantonese:
1.
2.
3.
4.