Translation:Sofia saw a man, who was standing at the corner.
I don't understand why you use "staras" here. It's past, so shouldn't it be "staris"?
Rule one of Esperanto indirect speech: don't change the tense. The same seems to apply here.
At the time of her looking, she would have told you: "Viro staras ĉe la stratangulo" - present tense.
So you can you tell someone about that later, you put the seeing in the past tense (since that has gone by) but keep the guy in the present tense because you are, as it were, quoting her. (Something she saw rather than something she said, but still.)
Sounds odd to a native English speaker but it's how Esperanto sequence of tenses works.