How can I check if black hat SEO is done on site or not?

On your website or others? 

Just go to your Google webmaster and see what links are inbound links to your website. Finding spammy links with no relation to your content is black hat SEO. It doesn't matter if you created it or not, this can still affect your website ranking overall.

Just go to your Google webmaster and see what links are inbound links to your website. Finding spammy links with no relation to your content is black hat SEO. It doesn't matter if you created it or not, this can still affect your website ranking overall.

You can use google webmaster to check black hat SEO. Look for spammy backlinks that are not relevant to the content, you will be able to find the website containing black hat SEO. If your website is identified with black hat techniques, your website's ranking will be affected. Tools that can be used to check black hat SEO are Moz SEO, Google Search Console, and Ahrefs.   

One of the first things you can do, is check a tool like Open Site Explorer, Majestic SEO or the Google Search Console Link Report. Each of these tools do pretty much the same thing, but I prefer Majestic. Majestic SEO will show you any spikes in backlinks.

If you're discovering hidden links or a lack of useful content on certain pages, these are clear signs of black hat SEO. It means ignoring proper content marketing practices and manipulating information to take advantage of high-volume search terms is an unethical strategy.

Keyword Stuffing: Look for excessive keyword use in content.
Hidden Text or Links: Examine the page's source code for hidden elements.
Low-Quality Backlinks: Check the backlink profile for spammy or irrelevant links.