Perhaps you should try some spelling variations:
ban thanh » ban hanh
toc sach » hoc sach, doc sach, thuoc sach
ban hang » ngan hang
hieu van » hieu va, thien van, lieu va
nang mai » nang ma, nang tai, lang mai
hieu ve » hieu va
sach ty » sach y, sach tu, sach thu
cam dua » ca dua, cay dua, chay dua
mai hoi » mai khoi, dai hoi, lai hoi
ty nang » ky nang, ty xang, ty hang
hai cuc » tai cuc, hai cua, thai cua
cuc tre » duc tre, cua tre, cuu tre

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach ty nang mai hoi. ((hieu ve) or (hieu van)) cam dua ((ban thanh) OR (ban hang)) hai cuc tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ty nang mai hoi. ((hieu ve) OR (hieu van)) cam dua ((ban thanh) OR (ban hang)) hai cuc tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ty nang mai hoi. ((hieu ve) or (hieu van)) cam dua ((ban thanh) OR (ban hang)) hai cuc tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ty nang mai hoi. ((hieu ve) or (hieu van)) cam dua ((ban thanh) OR (ban hang)) hai cuc tre*.