Hi Sandra,
Well you can buy an auction directly on skyauction.com or you can buy a vacation certificate (good at two different websites). I've done both, because sometimes the vacation certificate is cheaper or opens up more week options than the direct auctions on Skyauction.com.
As for the vacation certificates, the companies do advertise by region on skyauction, but really they can be applied to any region. They are mostly equivalent to low demand bonus weeks or getaway weeks on II and RCI. Once purchased, you will be given a code. You then take that code and apply it on Resortcerts.com or leisureloyalty.com good for a week's credit at those sites. IMPORTANT TO NOTE - MANY HAVE UPGRADE FEES. I'll explain below.
The $299 cetificates you see on skyauction are redeemed at Resortcerts.com (owned directly by RCI ). It's important to note that many of the resortcerts.com week options do have upgrade fees for specific weeks. Some don't, so make sure it's worth your $299 + whatever the upgrade fee may be before you purchase the certificate. You are able to search inventory first before purchasing. Once you find something you want, then buy the vacation certificate and immediately apply it since week availability fluctuates.
Last May, I stayed at the HIVC Oak N' Spruce Resort in Lee, MA using this method for a renovated 2 bedoom. Total cost was $299 +$20 Skyauction fee. Great deal at $319 total for the week.
The $279 certificates you see are redeemed at leisureloyalty.com (I'm assuming this is probably II, but they mask their real identity very well). They also have upgrade fees on more in demand weeks. Same rules apply. Search their inventory first.
This is an easy way for II and RCI to make even more money by releasing bonus weeks and getaway week inventory to the public without alerting their members who are paying for the opportunity.
You know there are other RCI portals you can use:
https://www.tripbeat.com/
https://www.endlessvacationrentals.com/
And if Military (though not sure it's really enforced)
www.veteransholidays.com
www.afvclub.com/