The women in a clothes shop who help people try on clothes and buy them and take commissions are called 'saleswomen' in a novel, The Cuckoo's Calling. What I want to know is do you call them with this term, 'clerks'? By this definition, a person whose job is to keep the records or accounts in an office, shop/store etc, it seems not used in the case, but I don't know exactly.
Where I live, the terms salesperson/saleswoman/salesman are certainly more commonly used, but I wouldn't think twice about it if someone used the term salesclerk. Both are acceptable and understandable. As to why the term "clerk" is used, perhaps it is because they are responsible for keeping a balanced register/till.