What is the difference between sales clerk and salesman?

A sales clerk is a person hired to work in a store where things are sold. Part of the duties of a sales clerk is to record sales on a cash register or equivalent devise, accept payment and make change.

The term "salesman" may be used in the same context as "sales clerk," but can also describe a person who goes to customer locations to convince them to buy a product. The salesman would take the order, but would not usually accept payment. That would be billed to the customer and the product would be delivered sometime after the order was placed.