Is this because WP is now blocking outside adds on free accounts? WP recent advised users that ads may appear on free accounts. I saw that WP has a plugin just for Amazon posts, but any plugin requires a business account. In looking at the pay-to-play WP account details, it looks like one has to buy the second level account in order to “monetize your website”. 

Two-tier programs exist in the minority of affiliate programs; most are simply one-tier. Referral programs beyond two-tier resemble multi-level marketing (MLM) or network marketing but are different: Multi-level marketing (MLM) or network marketing associations tend to have more complex commission requirements/qualifications than standard affiliate programs.[citation needed]
18. CraigsList – Some things don’t ship very well. Other things may make you feel uncomfortable to sell to someone across the country. Anytime you’re selling a large item or something you just don’t want to ship, Craigslist is a great place to go. It’s simple to list your item (again, take good pictures!). If you don’t like the idea of putting your phone number out there, the interested individual can send you a message to your inbox without even getting your email address.
File-Sharing: Web sites that host directories of music, movies, games and other software. Users upload content to file-hosting sites and then post descriptions of the material and their download links on directory sites. Uploaders are paid by the file-hosting sites based on the number of times their files are downloaded. The file-hosting sites sell premium download access to the files to the general public. The websites that host the directory services sell advertising and do not host the files themselves.
I have a free WordPress website with 1000-2000 visitors/month. I was trying to place Amazon Affiliate ad links last night and failed/flailed mightily. I would paste the links into my posts in the HTML mode, switch to Visual mode, and could see the image. However, every time I tried to save or update the post, the image reverted to the gangly hyperlink. As some suggested, I tried cleaning the links of any formatting from the copy and paste with text edit. No dice.
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