I agree with James... but if you place all of these links at the bottom of the page you will not make much money.

Also, consider who persists to the bottom of your articles.  They are your very best visitors and your potential evangelists and linkerati.  Instead of blowing them off to an affiliate site, recommend more of your content to them.

And... when your affiliate links are higher up on the page your less interested visitors or your highly distractible visitors will use them and you will make money as they leave - probably a LOT more money.

All of my best producing ads are high on the page and the bottom of my page is where I recommend more content.  I learned not to sell my most valuable visitors.

"buyparts.com doesn't work"

I don't want to give a response without having a clear understanding of this.

I don't have any formal testing to back these observations.  These are simply what I have noticed by experimenting with affiliate programs for twenty years.

**  I believe that google strongly dislikes "thin affiliate" websites.  These are sites that are monetized by affiliate links but that have very little real content or low value content.  I believe that they are subjected to a "quality filter" that is more strict than the "Panda" algorithm.

**  If you link to affiliate websites, expect those links to drive the affiliate site higher in the organic SERPs.  So, if you are competing in the organic against the affiliate program site, you will empower them at your own expense.

**  I have used Adsense on all of my websites since the first week that Adsense was available.  I've learned how much money different ad positions on the page can produce with Adsense, then I have compared that to what affiliate ads produce in the same position.  Adsense almost always make more money - not a little more money, a lot more money.

**  I have also compared the amount of money that I can make using affiliate links to the amount of money that I can make by stocking the product and filling the orders myself.  I make a lot more money filling the orders myself.  There is no comparison.

**  What I have not tested is how much can be earned by using hypertext affiliate links within the paragraphs of my content.  In those locations, I am using links to sales pages on my own website or to articles on my site that are relevant to the links.  I am confident that the sales links to products that I sell and fulfill myself will make a lot more money.  I think that links to my own article content are valuable, but if they are more valuable than a small commission, I can't answer - but I'd rather keep the visitor on my own website.

Keeping all of your business on one domain will help with your branding, since there is a natural overlap in buyers and sellers of auto parts.  It will expose your buyparts business to everyone to comes to the sellparts domain.

My preferred method would be to keep all of the pages in folders on the sellparts domain.  That is best for SEO purposes since Google does not give subdomains the full benefit of their root domain.  I would work hard or pay for development to make that happen.

My very last resort would be to use a subdomain.  The pages on the subdomain would not perform as well as if they were on the root domain.

Put links in the pdfs.  Edit their "properties" to optimize them for the SERPs.  You can place "buy buttons" in pdfs, include ads in them.  Track the number of views through log analytics.

Search here and here to get lots more information about using pdfs.

I am betting that this "author" is not authorized to be offering links for a fee in Huffington Post articles.

So, you might pay $1000 for this link and be told that it is permanent, but this person does not own the Huffington Post website, then the site owners or staff can take his article down at any time or remove this link at any time.

Also, if that author offers to make links for the wrong person and they report him to the Huffington Post, he will be fired, and all of his links will come down.

Ask him how the check should be payable and then you will find out if he is the link seller or if HuffPost is the link seller.

I still think that there is no problem with having title tags that match your H1 tags.

Ten years ago, I wrote title tags that focused on keywords.  Now I am writing title tags that focus more on presenting something interesting from the article that might elicit clicks.   A lot of the old title tags remain on the site but I revisit them every time I update or rewrite a page.

I think that Google knows what (keywords) your articles are about - so there is less need to stuff them into a title tag.

However, matching the keyword to what the searcher has in mind and will see bolded in the SERPs is still important.

"providing variety within the SERP when compared to other results"

Exactly.  You need to stand out.  Show that your content or product has special value, inspire the searcher to click on your page.  I believe that title tags can move rankings if you can get the visitor to click and hold them after they land.

Use both.

Breadcrumbs help search engines and visitors understand the structure of your website.

In-content links get clicked by visitors, and they might pass anchor text value to pages within your site.

The only safe move here is to create amazing content for both blogs - but why have 2 blogs? Why double your effort when you could be using all the content to prop up the main site?

Andy makes a very good point here.  If you have a good article about Brass Widgets on your website and you decide that you want to write a second Brass Widgets article to publish on another website, then you are going to publish a second article that will compete with you and take some of your traffic.

Even if the articles are slightly different or very different they will still be "competing" - either at the short tail keyword level or the long tail keyword level.   The result will be damaging to your traffic.  The amount of damage will be proportional to the strength difference of your domains and  the diversity of keywords in the articles.  If the second domain is a lot more powerful than your own domain you could lose almost all of your traffic to the second website.

I have a website that publishes only unique articles.  Some of those articles have been written by other people in my industry who have similar articles or entire websites about the topics that they gave me to publish.  I never asked any of these people to write an article for my website.  Every one of them came to me with an offer.  With content written by these other authors, my website frequently outranks their website for primary and secondary keyword of the industry.  They might have a website that is powerful for the topic, but I have a website that is authoritative in the industry.  It can be hard to predict who will win at different levels but my site now competes and brings in lots of traffic for topic areas where I have never written.

Publishing on your own site, as Andy suggests, builds the strength of your site and does not invite potentially strong competitors into your keyword space.   There are benefits of sharing articles.  You get exposure as an "expert" on another website, which might have amazing traffic that includes visitors who will seek you out to do business.  You can often get a link on those websites that  will send lots of traffic to your website.  The best situation for all is if you simply want to get your message out to as many people as possible, but if there are competitive concerns then you must weigh the value of a link with the value of the exposure and the risk of a very strong competitor moving permanently into your space.