Need custom comments functionality( beyond comment module) in drupal

I've already enabled comments module.

For my website i've following requirements:

1. Customers will leave comments about vendor service on Pages
2. Vendor will be provided a login who can reply comments
3. Only vendors will be able to reply comments

Also I want to restrict some words used in comment author names like "customer".

All I want to whether any module exists with this functionality or I need to do coding myself.

This is almost certainly a custom code job. Drupals default comment system allows anyone to with the correct permissions to comment on nodes.

comment_reply() will give you a starting block to achieve what you want.