Seems wrong, and illegal doesn't it?

It's not only wrong, it's illegal.

Is this an illegal activity for the wholesaler, the mail man/bird dog, or both?

If the broker is holding onto your money, he/she may have illegally appropriated your funds and no longer have the funds to return to you.

A SFR market emerges that looks like this: crappy houses that can command a high rental price by packing students in, often in illegal structures, basements, converted garages, trailers, vans, tents, whatever.

Real world experience and applications is from investors who have done and are doing what you are talking about and are contemplating doing.The people that have done something will have a much different view from those who have just read about things.It's kind of like workers at a restaurant complaining that the manager has it easy and never does anything.

I live in philadelphia and bandit signs are illegal here.

It is not illegal to pay any item outside of closing, paid outside closing (poc), so long as it is fully disclosed.

I realize the people we manage are not professional, rather blue collar workers that can make it more complicated than needs be, but the principles are the same at a smaller scale.

Companies have decided to cut their overhead by not providing a brick/mortar building and having their workers provide equipment like computers.I saw positions from companies looking for people to answer emails or field phonecalls.