Adding Tags to Posts - Black Hat Technique? Safe or Not?

Hello, i heard a SEO Specialist that said to me that adding tags to posts will cause a duplicate content.
For example, if i have a post let` say with name Dog Training. If i add 5 tags to it: Dog Training, Dog Training Free, Dog Training Amateur etc. it will help in SEO and in Traffic or will cause duplicate content?

Tags are natural, so use it. But tags like "Dog Training, Dog Training Free, Dog Training Amateur" looks spammy, so better use "free, amateur" and other tags relevant to article

Add tags and download a plugin putting a noindex/nofollow to tags/category pages. I don't remember the name on the plugin. But it's free .

You could add the tags in your posts by making it look natural, not spammy. But if you're a blackhat, who cares about natural posts. But of course, there are repercussions.