attendant
An attendant is someone whose job is to help people in a place such as a petrol station, a car park, or a cloakroom.
She stopped the car and asked the attendant to fill it up.
Someone who works in a shop selling goods to customers is not an ‘attendant’. A person like this is called a shop assistant.
I asked the shop assistant for a receipt.
In American English, this person is called a sales clerk.
She worked as a sales clerk in a record store.