Are the products discontinued or out of stock? In my opinion, the 404 errors are only detrimental to your SEO when they are in an overabundance. Relevant 404 errors are important, not just for Google, but for the searcher as well. They need to know that a product has been discontinued. If a product is just out of stock, I wouldn't 404 it at all.

This is a video by Matt Cutts on how Google handles 404 errors. https://www.youtube.com/watch?v=oya9Pl7ukNo

Hi there,

I work for a rather large supply company as well. When we have large items go out of stock we repurpose existing pages to advertise new pages. If it is a small product, like a part or something, we 404 the page.

This is an example of a repurposed page: http://www.apelectric.com/6241-Generac-Guardian-Series-14kW-p/6241.htm

404 errors are not a negative thing per say. Of course you don't want hundreds of them because it creates a negative user experience. If a product is truly discontinued, it is better to let the searcher and the engine know that. No following the pages isn't the best idea because it can prevent traffic from getting to your site. We have about 87 404 pages and they have not influenced our organic rankings. I don't recommend 301 redirecting product pages because it can be misleading to the searcher. For example, we rank really well for the Generac 6241. I wanted to 301 that URL to the replacement model, but if someone types in Generac 6241 and lands on Generac 6461, they are probably going to bounce right off the page. That is not good either. One thing I have done in the past is redirect the product page to a related category page. So, the Generac 6241 could have been redirected to the Air Cooled Generators page. I think this was the better way to do it however.

If a page has value, and can be used as a way to direct traffic to another source that is my favorite way to handle discontinued products. At the end of the day, a $15 part doesn't justify the amount of time it will take me to redesign the page, so I let it become a 404 error.

This is a video from Matt Cutts at Google on how they handle 404 pages. https://www.youtube.com/watch?v=oya9Pl7ukNo

Generally, optimizing a page means that you are targeting a specific key term you want to rank for. While you might not see measurable "negative" SEO effects of having pages with no content, I believe that you could use those pages to target key terms. Images rank as well as pages. You can use image alt attributes and add some content to those pages which may help drive some traffic. I like to play safe rather than sorry. It takes a little bit of work, and you might not have keywords for those pages yet, but you could use the images as ranking tools.

They have different purposes, but all relating to preventing the same page from showing duplicate content because of the different ways a URL can be written. There is nothing on this page to show that using a canonical tag can take two different pages and remove the similar content. The purpose of the canonical tag is to set the preferred URL for one page.

I would remove the domain name when you use the query.

moz keyword research in the united states best practice gets a much different SERP than keyword research in the united states best practice.

If you are trying to get a pure SERP result than you shouldn't use your domain name. That will tell you if there are any other search results in the web. If you want to find duplicate content on your site use copyscape.com or go to GWT and look for internal duplicate content.

Again, not only copy creates a duplicate content message. It is having an off html to text ratio, repetitive links in the HTML with not enough copy to balance it out. If Moz is reading a duplicate content error, and the number is increasing week to week I wouldn't discredit the finding simply because you don't understand why the error is occurring. The canonical tag won't prevent two different URLs from showing duplicate content. If you want to do that, no follow one of the URLs. That isn't best practice though, best practice is to fix the copy.

Canonical tags just point non www URL address to www addresses. It tells the engines that whether or not the WWW is used, the two URLs are the same page. It will only solve the duplicate content errors if that is in fact what is causing the error. If the actual cause is duplicate content the only way to solve it is to write unique copy.

Depending on when you made the changes, it could just be that they weren't fixed in time for the next crawl. Fixing these duplicate titles are really important for your SEO.

Open the medium priority issues and set it to duplicate page titles only. When you do that you will see which titles are duplicate. Sometimes there are more than one duplicate title so make sure you completely expand each line. I would make sure I go back into all of them and see if what is showing as duplicate on the crawl report is still the same information on your title tags. If it matches, then those pages need to be changed. If the titles are different, then wait another week and just see if the timing was off somehow.

If you have pages with duplicate content there could be a few things triggering it. There could be a too much of the same HTML and not enough text to make the pages look different. The content on the pages could be very thin, and very similar. The best way to offset duplicate page errors on your site is to get original, informative, unique content on those pages. You can set your crawl report to high priority errors, then select duplicate page content. You can then look at all of the duplicate pages side by side to determine if you can get unique content on those pages. If you are getting duplicate page errors for the same web page, one with a WWW and one without, then check to make sure your REL Canonical tags are in place and functioning properly. If the pages are different then you need to get great content up.

In my experience XML is really the best practice. You can have more than one site map technically, but you should always have an XML version.