Other people seem to be totally unaware, they couldn't spot a snake oil salesman if they had to.By understanding others, "seeing" their motivations can help you "see" yourself.

He charges $75 to do the repair and even fixes the shelf in the next room.I have another vendor #4 who doesn't have a snake to do this kind of job, but he's usually around and can diagnose the problem and let me know what's really going on with it, as I am rather busy and often have to take the word of the tenant and photos etc to find out what is wrong.

He respected his tenants and they respected him also for showing up and fixing stuff ASAP.. although he tended to draw the line at clogs and had a great plumbing snake company for those and the occasional sink..but he knew his strengths and wasn't afraid to say he was the owner. 

There are snakes in this business and that is a sure fire way to find out who they are. #2 You answered your own question already.

There are true professionals out here on BP, and there are also weasel guru snake oil salesmen, and it honestly sounds to me like you are not yet able to sort out the two.

Also, working with a buyer's agent can be helpful because as long as your agent is worth their salt they will help you know when the listing side is selling you snake oil. 

I have no clue who @Nick Vertucci is other than an RE trainer of some sort, but just because he charges to teach about RE investing, doesn't mean the guy is a scammer or a snake.

Darryl already stole my thunder, but I tend to disagree with him a bit on this point.

Unfortunately the profession is sullied by a disproportionate share of quacks, charlatans, and snake oil salesmen.

($50 or elbow grease), interior doorknobs if the old ones have flaking or deteriorating look (~$8/apiece), a few snake plants for the interior/exterior (<$15 - impossible to kill).