I don't have an issue with enterprising and intelligent people getting their hands on hard-to-find owners manuals or repair manuals that are out of print and putting them up for auction at a premium price. Let's say you buy an old motor that was built so long ago, the company doesn't offer ANY support or downloadable guides/manuals for the item. You *need* the information in these guides to maintain or repair your item, and sometimes the only way to get it is to buy an old manual from someone else. If you are shopping for a specific rare or hard-to-find manual, there are a few important things you need to know BEFORE you place your bid ...

1. It is a violation of copyright law to scan or photocopy any company's owners manual or repair manual for resale (unless the manual is more than fifty years old). Frankly, if you are buying a "manual on disk", you know right off the bat that you're dealing with an illegal copy. Whether you choose to go through with your purchase on so public a forum as eBay is up to you ... and not much different than buying a Rolex for twenty bucks from the shady guy in the park.
2. Make absolutely CERTAIN that the disk you are purchasing is compatible with your computer system. Examples of auctions out there now include manuals on 5" floppy disks (nobody has one of these drives anymore!), manuals scanned and encoded with software that does not produce a universally-readable document, and disks your system just plain can't read.  If you get the disk and can't read it, will you get ALL of your money back? Even if the seller says yes, don't count on it.
3. Be aware that once you get the manual, they are often scans or photocopies (or scans OF photocopies) of such low quality, they are impossible to read. It is becoming increasingly common for one scam artist to con another, who in turn replicates the scam to make their money back ... and then some.

Unfortunately, in cases of "manuals on disk", you can't typically go by feedback unless the feedback is specific to the manuals they have sold. I purchased a repair manual on disk for a vehicle for which I could locate no printed manual ANYWHERE.  It took three weeks for the manual to arrive. When it did, I saw that it was the wrong manual (it was for the same manufacturer's line of trucks, not passenger vehicles). I contacted the seller, who told me to just send it back, and he would send the correct one. I sent it back, and guess what? Never heard from him again. By the time I was sure I'd been scammed, it was too late to report it to eBay or Paypal. Live and learn.

With a second manual I purchased online, it was for an antique appliance. I needed to understand the mechanisms that made the appliance work, so I HAD to have a copy of the original owners manual. How LUCKY I felt to have found one on eBay! I received the manual - on a disk my computer could not read, and four other computers in the house couldn't even recognize as formatted.  Was there ANYTHING on that disk?  Maybe. Maybe not. Maybe it had been magnetized during shipping ... or maybe it was a 5¢ blank disk I'd just paid $15.00 for!  Once again... by the time I realized I was getting scammed, it was too late to file a complaint with eBay or Paypal that would get me a refund.

When it comes to out-of-print manuals, always do your best to find the ACTUAL printed manual. As soon as you start looking at manuals on disk, you are looking at a very high probability of trouble with the seller, not to mention certain infringement of copyright law.