UTTER BULLSHIT!
This guy has no idea what he is saying.
Agreed. That jumble of words actually does mean something. More than 95% of my income in the last 5 years has been the result of successfully completed verbal contracts, many of which do not even include a handshake. About half of the customers that have insisted on a written document have made some efforts at cheating me. In the beginning, some succeeded. There's no paper in the world that can protect you from an asshole that is determined to screw you. Real wisdom came to me the day I realized that I cooperated in every screwing I got. The only power you have is in your analysis of the situation, and the decisions you make based on that.
There's no "magic bullet", "one size fits all" formula. If a guy feels wrong, don't do business with him, or name a too-high price and scare him off. Get half up-front. Make certain he doesn't get full value of what you are doing until you get full payment. But consider, all these "protective measures" have a dynamic of "diminishing returns". At some point, it's more hassle than it's worth. If you are going to put a lot of effort into trying to guarantee that a customer that you don't trust will pay you, you could put that same amount of effort into finding a customer that is trustworthy. The world is chock-full of customers, more than anyone could ever take care of. The trick is making the connection with the RIGHT ones, and avoiding wasting time and energy connecting to the wrong ones.
And if you really can't tell the difference between the two, you shouldn't be self-employed anyways. This is the free market, and it's a hostile wilderness. Sheep get shorn, suckers get taken and fools and their money are soon parted.
Most people get screwed because they fail to take full responsibility for the consequences of their own decisions. They blame everyone but themselves for everything that happens, and the end result is that they fail to learn and develop the skills needed to differentiate between who you can trust and who you should not.
I remember VERY clearly the time I asked a customer for a partial payment for a job that was almost complete. He walked away like someone had jammed a large stick right up his ass. I noticed it, but did not see it for what it was. It was a warning. That reaction was a physical manifestation of his deep aversion to paying people money for any reason. I was surprised when he gave me a lot of trouble when it was time to pay, but I shouldn't have been. In retrospect, it was obvious. He simply HATED paying people anything for any reason. (I found out later he did the same thing to everyone that ever did business with him, which was why & how I was hired; no one else would work for him so he had to find someone new, that didn't know him or what he was like.)
Yeah, there's another thing they don't teach you. You should always be aware of the question "Why me?" when doing business with someone. When they can hire anyone else on the planet, why is it YOU? Is it your handsome good looks, your candy-flavored sphincter, your cheap price, the fact that you were the first one to answer the phone, or is it because you are the only one dumb enough to do business with an asshole?
It's important to ask this question, as sometimes a correct answer can either save you from getting screwed or (conversely) it can also help you to make some good money.
Finally, here's a little tidbit for anyone that doesn't know this. Answer the phone. That's money calling. It's not good enough to finish wiping your butt and then calling the person back, because they are working a list online and will already be talking to someone else. Answer the phone, and make certain you don't flush until after you've done your business. No one wants to know they are doing business with someone sitting on the toilet, and you don't want to lose any money because the phone rang while taking a dump.