Salaam & Greeting

Women kissing each other on the lips when greeting

Q: Two married women who are friends kiss each other on their lips as a form of greeting, is this allowed? They argue that they have no desire or lust but only sisterly love. Is this possible? Sometimes their mouths are open too. I believe it is haraam. 

1. Isn't kissing on lips for two females haraam and sin 

2. If they kiss with their mouths open (not deep kissing though) it is bigger sin and haraam

Making salaam to people who we don't know whether they are Muslim or not

Q: Nabi (sallallahu alaihi wasallam) instructed us Muslims to give salaams to those whom we know and those whom we don't know (among the Muslims). How will we know the individuals we are giving salaam to are Muslims or not since we don't know them? Do we just assume that they are Muslims by looking at their clothing, their professions (halaal butcher) or any signs that would be hint of their faith or do we just ask them before giving them salaam?