If you are getting value from attending REI meetings, that counts much more than any endorsement IMO. 

Publications say they don't endorse ads that they run.

This is how its done in China  I was just in a  CE class for my Oregon brokers license that I hold and I am getting the CiPS endorsement which is a 5 day course and gives me a designation as A NAR Certified international property specialist...

A guarantor usually signs the original agreement, the parties to the agreement can simply refer to them; the undersigned as principals, endorsers and guarantors or similar wording might be used, in the signature lines they sign as guarantors they don't need to be under another agreement, that's a waste of ink and paper. :)

Most people especially millennial's (I know many Y,z and baby boomers that thought the same) endorse and support AirBnB.

A co-signor (endorser) is a signatory to the contract (lease in this instance) and is entitled to all the rights and subject to all the obligations of the contract ... in other words, they have tenant rights.  

Rich, I'm sure that it is harder to fool you than it might be a new investor that is looking for help anywhere they can find it.Maybe can use the endorsements better.

I'm in the process of conducting my own due diligence on Auction.com and considering Andy Chu's result, this is a big endorsement for any investor.

I am disclosing that I do have a California Department of Real Estate License with a MLO Endorsement.

As noted, I'd verify ALL I&E with an actual sheet seller is willing to endorse.