One can't help but wonder, on the basis of the volume of mini's that appear to have been sold so far, how the dribble of mini sales here, on eBay and various other places could possibly warrant any real concern.
I'd say that a few people bought minis in the hope of selling them at a profit (as per the original iPod minis), some bought minis on impulse simply because they were cheap, and then discovered they are really nothing special - just a Mac in a small box, some bought them and have discovered limitations caused by the lack of upgradable options and thus want to sell, some bought them because they wanted to try MacOS but discovered they don't like it, some bought them because they wanted a Mac and liked it so much they then bought an iMac and need to sell the mini to help pay for it, and some have found problems such as the Seagate drive noises, or dim video output with some monitors and decided to sell as a result.
One way or another, the number of people selling because of problems is likely to be quite small.