I wouldn't point fingers at bad advice, I'd just say that there's a pretty wide range when it comes to the value of used equipment. Not only that, getting in front of buyers is the biggest factor.
If we had a way to instantly connect a seller of a piece of machinery to every single interested buyer, then everybody would get the true market value for their machine. Outside of that, it's a bit of a crap shoot when it comes to what one platform versus another will drum up in terms of bids and buyers. List it on eBay and maybe that week you find a buyer, or maybe on another site you list it for three months and nothing.
FWIW we now have a Tractors & Equipment For Sale group associated with our Facebook page that in time will be linked to our site as it grows in terms of popularity. About 600 members now and counting. There are dozens of for sale groups on Facebook and as you found, some are great. If only they were all unified instead of broken up into many different groups with different levels of quality.