What guidelines we have to follow while giving sales pitch to a random customer or how should we proceed sales pitch to a random customer?

first, you should identify the current mood of the random customer very quickly during the greeting, and that is by focusing on his body language and voice tone. second, you shouldn't begin the pitch only if the customer mood is positive. If the mood is negative, you have to bring it back to normal in a very kind and friendly way.

never lose the customer :)