Is it permissible to return a greeting to a foreign woman, and how should one interact with her if she is a saleswoman in a commercial store?

Some scholars dislike the returning of greetings to a young, non-mahram woman, due to concerns of temptation and the presence of Shaytan, whereas the Shafi'is deem it forbidden. There is no harm in a man speaking to a woman out of necessity (such as for trade), provided he lowers his gaze, avoids seclusion, refrains from softening his speech, and limits the conversation to what is necessary.