早急です！チップ（gratuity）とPort service feeの違い

service

OXFORD
service
n.
1 the action or process of serving. an act of assistance. a period of employment with a company or organization: he retired after 40 years’ service. (often in phrs in or out of service) use for a particular purpose. (often in phr. in service) employment as a servant.
2 a system supplying a public need such as transport, or utilities such as electricity and water. a public department or organization run by the state: the probation service. (the services) the armed forces. (services) chiefly Brit. a motorway service area.
3 a ceremony of religious worship according to a prescribed form.
4 a set of matching crockery used for serving a particular meal.
5 (in tennis, badminton, etc.) a serve.
6 a periodic routine inspection and maintenance of a vehicle or other machine.

ここでは2の意味でしょう。
port services：港湾業務　空港と解す。

勤務、勤労、雇用、業務
〔バスなどの〕便
官公庁業務、公共事業、公益事業 ・・・

要するに有形の商品でない無形のもの（財）

service charge：サービス料、手数料
OCFORD
service charge
· n. an extra charge made for serving customers in a restaurant. a charge made for maintenance on a rented property.
feeはpaymentとなっています。