This is a literary style. More normally, it would be worded as ... once upon a time, two salesmen came to Seri. They sold pots, pans, and handmade trinkets for a living ....

In addition to having an "old-fashioned" sound, it also changes the word order so that you hear and think about someone arriving before you learn who arrived. This creates a certain anticipation and parallels events in real life, where you may be aware that someone or something is coming, and have a feeling of excitement and anticipation. Changing word order is a tool writers can use to produce an artistic effect. Another reason for doing it could be to create a rhythmic pattern to the words.

We see this structure a lot in old English but it is not used in modern English. It means that there were two salesmen and it is implied that they came from somewhere else (other than Seri). We often see this type of language in the Bible.

That 2 salesmen came to Seri. It's just another way of saying it commonly used in stories/ novels. You can also say: Once upon a time, two salesmen of pots and pan and handmade trinkets came to a place called Seri

It means "there arrived" or "there visited" as in "there arrived two salesmen" with "there" referring to the place called Seri.