Sales is, was, and always has been, a numbers game - and the most important number when it comes to being a successful salesman (in the sense of getting paid) is the number of phone calls made and/or new contacts met in a day.
My 'hit rate' or 'closing rate' can be 1%, and some other guy's could be 10%. But if I talk to 100 people a week and he only talks to 10, we'll sell the same amount (all other things being equal, which they almost never are.) Because I understand this, I can kind of appreciate the guys who are really hustling, even if it's only making phone calls. If you think it's easy, pick up the phone and call strangers for the rest of the day trying to get them to buy something you're selling. You better have thick skin for all of the guys (like most of us) who pick up the phone.
That said, when I was still in sales I was a big believer in the Zig Ziglar approach: integrity is your greatest asset as a salesman, and you can't be truly successful selling anything you don't believe in. Obviously not all salespeople are believers in this - or more likely, not many are.
As to what you think of as a ridiculous low-ball offer: I happily pay $5 for a gallon of milk at the corner store on my way home instead of driving 5 or 10 minutes out of my way and walking through the entire grocery store to buy it for $2.50 - it's a convenience I'm happy to pay for, and I come out way ahead after factoring in my time.
If, as a shop owner, you start putting a dollar amount on everything you do, you'll be amazed at what you spend your time doing. A 'big' company would probably use $100+/hr for a manager/executive at a small-shop owner level person (the billing rate for engineering or project management, including overhead, in the automation world is typically $100-$150/hr.) So when you spend a week (or a lot more than that, broken up over the course of months) of your time selling a used machine to get top dollar, subtract $4,000 from whatever you sold it for. And it takes your time and attention away from the things that actually matter, of course.