He did it through (1) professional website (2) constantly optimized for SEO (3) new social media articles at timely intervals (4) sponsorship of charitable events (5) ongoing public relations campaign (6) billboards (7) advertising in local newspapers (8) SEM .  

However, the seller claims he purchased the property as a two-unit dwelling based on Baltimore City public records, yet it’s not legally permitted as such.

Would these be found in public records? 

There just isn't a lawsuit or publication of events.I don't know what state you are in but some states require the bureaus to give consumers a free credit report once a year.

Most very successful STRs seem to have direct booking options, they are opening their properties to the YouTube Airbnb influencers to get more publicity, they are creating regular content through their own social media channels, etc.  

I always steer clear of Angie's List, Yelp, BP Vendor, Dave Ramsey Select Vendors, or any other service that charges the vendor for membership and then promotes the list to the public as if trust, excellence, and performance have ANYTHING to do with the list selection. 

what is your guys take on hiring Public adjusters to increase amount of claim?

If you want people to take you seriously in a public forum then know what you're talking about before you share your opinion.

And from public record the 4 or 5 I looked at are/were REO purchases as they state.With the amount they seem to be making (with the claim "without doing any of the work ourselves") in their business, why would they bother with seminars?

And if you don't like someone challenging what you put in words online, don't write anything publicly.