If a website loads a product on the back end but does not publish it for the public yet, can I access that information?
I see two questions here: 
1)Can I access information on the webserver that isn't sent to the client page? 
No. You can only scrape what exists on the page. Anything else would be illegally accessing a non-public server and goes beyond scraping into hacking.
2) If the site loads asynchronously and/or dynamically, can I access the content that loads after the main portion of the html?
Yes, using browser automation tools like selenium, you can approximate a user experiencing the site and wait for the full content to load before you scrape it. This is different from simple requests/beautifulsoup, which only gathers the HTML at the point when you send the request.
I'm new to web scraping and am trying to learn more. I know some websites load products on the back end before they make it available to the general public. Is there a way I can access that information using an HTML parser or any other library?
I suspect the website developers use dynamic javascript to alter the information after loading. Or use different tags/classes to hide the information?