Perhaps you should try some spelling variations:
hang vai » hang va, hang tai, hang hai
ban hang » ngan hang
tu sach » thu sach, su sach, te sach
cac dac » cac dan, cac dai, cac bac
vai cua » dai cua, hai cua, lai cua
cac duc » cac du, cao duc, cac nuoc
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang
o hoi » co hoi, o hoc, o hai
x hoi » xa hoi, x ho, 5 hoi

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach y nang ((x hoi) or (o hoi)). hieu ve ((cac duc) OR (cac dac)) ban hang vai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y nang ((x hoi) OR (o hoi)). hieu ve ((cac duc) OR (cac dac)) ban hang vai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y nang ((x hoi) or (o hoi)). hieu ve ((cac duc) OR (cac dac)) ban hang vai cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach y nang ((x hoi) or (o hoi)). hieu ve ((cac duc) OR (cac dac)) ban hang vai cua tre*.