A piece of cake

• theatre

• arcade

• circus

• cinema

• canoeing

• kayaking

• surfing

• snorkeling

• travel agent

• real estate agent

• marketing agent

• agent P

• pharmacist

• prescription

• nurse

• custodian

• headache

• toothache

• backache

• stomach ache

• convenience store

• grocery store

• department store

• booth

• sales assistant

• sales clerk

• sales representative

• commodity

• supplies

• ware

• inventory

• library

• auditorium

• cafeteria

• dormitory

Choose the odd one out

• consumer

• merchant

• client

• customer