To tend is used in the sense of watching over/looking after something/someone. For example:
Mr. Allen tended his garden. (He looked after all the needs of the plants, such as watering, pruning, weeding, feeding, keeping pests away, etc.)
Alice tended her sick grandmother. (She stayed with her, making sure she had everything she needed.)
So, in your example, the salesperson could help or assist you, but not tend you.
People also use the expression 'to tend to' something.
"Excuse me, please. I must go tend to the food I have on the stove before it burns."
Alex tended to his chores before going out to see a movie.
Used this way, it means to take care of a responsibility.
- For Teachers