Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
ban hang » ngan hang
nam dua » nam da, nam cua, nam mua
dua ban » dia ban, cua ban, qua ban
sach ky » sac ky, sach y, sach ty
hieu va » lieu va, hieu qua
mai hoi » mai khoi, dai hoi, lai hoi
vai ca » vai cac, vai cua, vai va
va nam » van nam, ha nam, va nay

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

• Performing a fuzzy search may retrieve terms with similar spellings: thu sach ky nang ((mai hoi) or (ma hoa)). hieu va nam dua ban hang ((vai ca) OR (bai ca)) tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ky nang ((mai hoi) OR (ma hoa)). hieu va nam dua ban hang ((vai ca) OR (bai ca)) tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach ky nang ((mai hoi) or (ma hoa)). hieu va nam dua ban hang ((vai ca) OR (bai ca)) tren".
• Adding a wildcard symbol may retrieve word variants: thu sach ky nang ((mai hoi) or (ma hoa)). hieu va nam dua ban hang ((vai ca) OR (bai ca)) tren*.