Because tenants would always want to argue over how much they owed.

That is considered brokering without a license and the punishments vary per state.There are many legal ways to wholesale, getting your license is just one of those ways.You also stated that the seller would not allow any contingencies (sounds like a smart seller) and that you did not want the seller to leave you hanging, I would argue that if and when you locked it up and did not find that buyer, then used your escape clause, it would be YOU leaving the seller hanging which is why he or she made that comment to you in the first place.

I took the haircut, I argue the stock market is due for a haircut also.

I've been there, it was before the pandemic and the case can be dragged on for months by the tenant just saying they need to get a lawyer, "abc" happened (insert reason) and the judges will grant continuances at least 2 times from you initial court date which means at best case scenario the judge will hear your case on the 4th time back to court typically with 1 month between court dates.  

I would argue his advice has hurt virtually nobody, but how many people ended up in financial ruin after seeking a get rich quick scheme? 

Although I would not support unregistered guests staying in the Airbnb overnight or throughout the entire stay, I would argue that it is unrealistic for you to expect that people (guests and their friends) are not going to be coming and going when they’re on vacation or whatever.

I would argue that your website at the stage your describing is a place holder for you. 

There are a many that can be argued as the most important. 

If it could be argued that you violated the owner's right of redemption (robbing them of the equity they could otherwise realize through a private sale or foreclosure), you'll likely get sued and lose.

Those arguing to just blow em off in 1 form or fashion, lol, well I am blunt and compulsively honest so I will just call it as I see it that they have no clue what there talking about, that's a fast-track to more problems.