The point of that paragrapgh is that "You aren't going to get rich metal detecting" and it attempts to point out some of the other aspects of the joy of detecting, like the thrill of the hunt and having a nice collection to show and tell. Not "Don't ever sell any of your stuff".
And like the book says, if you try to sell it to other than friends or friends of friends (or as in my case to coworkers) you won't get what the stuff is really worth. Well that's very true. But I HAVE sold a lot of things to coworkers. Mostly because after doing this for over 6 years and not ever selling anything, I realized that if I do it for another 6 (or 16 or 26) years then what I will eventually have is this huge collection of stuff. To do what with? And when I would show things to folks at work, they were asking me "Ooh...how much do you want for THAT? How much for THIS? I have to have THAT! Please sell me this." So I began to set reasonable prices for some stuff, mostly not to be giving it away, but very good deals. Because to me, the fun and the thrill was in the hunt. Once the stuff was found, if my wife and daughter didn't want it and I didn't want it and somebody at work DID, I would sell it. And then I put the money back into the hobby. I bought a new straight shaft. A new scoop. A set of scales. A detector. And I'm about to buy the diamond tester I want. So in that way, I can turn some of the unwanted finds back into finding even MORE stuff that I don't need.
So no, it's not about the money. It's about the hobby. And it's about letting the stuff go back out to somebody who can enjoy it. I get all the "I'm the man" feeling I need from showing it off one time here on the forum or at work and then what do you have? There are different things that motivate people to do what we do. Sometimes it's "because it's there", like why do you climb the mountain? Other times it's money or the thought of riches. Many times it's adulation and approval...the "look at ME!" angle. Which we have to suppose is your motivation, since your very first post in this forum was
"Ha! Got You ALL Beat! Look At THIS!" Where you proceeded to tell us how you just got your detector and showed us a wealth of finds that many will never see in a lifetime. I found your "bravado" a bit of a put off...it was like you were taunting us. I kept my mouth shut though, because I told myself that there were different reasons that people got into this hobby and they may be different from mine.
All I know is that I love to metal detect and I've spent as much time digging up pieces of lead from 1863 as I have gold rings. I haven't sold ANY of that. Can't find anybody that wants to buy some lead.