Correct Option: A

amateur (Noun) : a person who does something for enjoyment, not as a job
professional (Noun) : a person who does a job that needs special skill/training and a high level of education ; a competent person tradesman (Noun) : a person who sells goods ; shopkeeper labour or
labourers (Noun) : the people who work for a country/ company/factory, etc.
customer (Noun) : a person/an organisation that buys something from a shop/store/business