Sometimes the words are used to describe the same type of work in a department store.

Normally a 'sales assistant' refers to someone who works in a shop and sells things to customers. (It means the same as shop assistant) A salesperson is someone who either a) sells goods or services to the public or b) sells products or services to shops or companies on behalf of a company

A salesperson is someone employed to sell goods or services. Assistant is someone who helps or ''assists''. You can get a Sales Assistant. This means, that person will help the person who is a salesperson and work under him. The salesperson will be of the higher rank i.e. the boss of the sales assistant.

the different is that the salesperson is specified in sales while assistant is large: he maybe assistant in any matter or duty (within sales departement, or communication depatemement..etc) salesperson = a person whose job or duty is to sell his goods to particular people or professionals. assistant = a person who helps in finishing tasks (maybe related to any professional field, management, sales, financial, engineering....etc