It is unethical to sell a problematic player and not mention it in the ad. It will lead to nothing but trouble, for everyone involved. Yet people do it.
The first used sacd player I bought in 2007 failed to read the first 3 sacd's I tried. Seller then claimed the player had worked perfect for him. He either only played rbcd's or was a liar. It was easiest to just send the player to Marantz Service and get it fixed. Disputing a sale, even on Ebay, gets pretty long winded and tiresome.
While people can surmise that owners of SA-10 and Ruby have had laser issues and not post about them is fine. But it is not first-hand knowledge of such. The laser mechs are also sold to high end companies dcS and Playback Designs. That in itself does not guarantee flawless operation, but it does ad credibility to these being very good laser mechanisms that won't have the issues of earlier sacd lasers.