A new trend in spam is to duplicate legit comments from your readers to hopefully pass spam filters. Spammers post content that was previously approved on your site, but with their own name and URL. This plugin prevents this.

Ozh' No Duplicate Comments

Prevents spammers from duplicating legit comments but with their commenter name and URL

Skip the login form: every visitor automatically auths as an admin. FOR ‘LOCALHOST’ TEST SITES only, obviously, like when designing a plugin or a theme and testing it across various browsers.
For a hassle free integration, drop the plugin file into <code>wp-content/mu-plugins</code> (create the directory if needed) and it will be automatically activated.
For live blogs, see <a href="https://wordpress.org/extend/plugins/always-remember-me/" rel="ugc">Always Remember Me</a>
<h3>Support</h3>
On <a href="https://github.com/ozh/no-login" rel="nofollow ugc">Github</a>. I don’t read WordPress support forums.

No Login

Skip the login form and always auth as admin. FOR TEST SITES.

Ozh' No Duplicate Comments vs No Login