Question, are the terrible reviews about SkyAuction itself, or about the units or resorts that were booked?
SkyAuction primarily just wholesales "leftover" vacation interests (timeshares primarily) from various resorts. There are a lot of things that can go wrong when you start adding parties to the rental chain. A lot of SA's listings are leftovers from RCI and II, so you are now 2 parties removed from the resort. You -> SA -> RCI/II -> Resort system. However, for the killer pricing, it is probably worth a little risk, and your experience will probably be much better when dealing with a larger upscale branded resort than with some of the smaller indie resorts.
If I didn't already own more timeshare interests than I can use, I would probably be all over SkyAuction for my bookings.