冒险娘之旅 China 发票 in Restaurant

During my china trip, I noticed a lot of customers would request 发票, tax invoices from the restaurants. Out of curiosity, I asked my new found Shanxi friend why would they want the 发票. Personally I thought this practice was a waste of paper. Sometime the 发票 came in a few pieces of paper. My friend explained that it was 公共义务, a citizen's duty to prevent the restaurant from avoiding tax. Uh-ha, that explained all. Once a 发票 was issued, the China government would be notified of the purchase, liked GST in Singapore. What a righteous thing to do, I thought. Then I asked further, if the restaurant refused to issue one, what would they do? Do they report them perhaps? The answer was funny, if no 发票 was given, they would then asked for a discount for the meal. And they would preferred a discount then a 发票 obviously. Duh...