Yeah, most of the time, the sellers seem to have bought the item just to sell on for profit and have never actually used them. They say they have been tested, but the majority of the time they have just simply powered them up.
Humax machines have all sorts of quirks / faults which can take several days of constant playing, recording and playback to show up.
I have seen several Humax PVR-9300T been sold recently. I suspect a good majority of them will have the skipping during playback fault just like my very own 9300T has. The sellers might well have tested them and genuinely think they are fully working. The trouble is the new owner wont find this fault until they record and play back certain programs. If there were a genuine trouble free 9300T for sale on Ebay, then I would snap one up for myself.
There are some real jokers though. That is the reason I am hesitant about buying another box off Ebay. Your tips for spotting the difference between the HDR-FOX-T2 and the Youview DTR-T1000 will certainly come in handy, though.