Double Ten National Day Shopee Day

Yesterday I was browsing Shopee and bought the lighter I wanted, plus a lazy phone holder. After searching and searching, I finally found a really peculiar method! Buying just one lighter with shipping cost 78 NTD. Later, I bought four lighters plus a lazy phone holder, and the total was 101 NTD, with no shipping fee. It felt like the more I bought, the cheaper it got, so cheap I couldn't believe it. Has anyone here had experience 'wool-gathering' on Shopee? Write and tell me, thanks.