Methinks you're missing the point, mon ami.
1. Yes, it is O.K. for people to post THEIR premium themes - designed and vended by them - here. Nevertheless, there is a marked difference between selling your own work and reselling someone else's on another person's web site. It sets a bad precedent and raises questions about bias.
2. I think the best way for a person to determine whether a theme is good or not is to:
A. Test the demo on the designer's web site.
B. Read the comments to see what others have to say.
C. Ask any questions you may have about the theme in the comments section.
D. Click on commentors' links in the comments section and see if they are using it.
E. Contact commentors on their web site and ask their thoughts on the theme.
3. No one said that reviewing premium themes is prohibited on Weblog Tools Collection. However, sponsored reviews and reviews containing affiliate links to purchase themes or plugins are prohibited.
4. You're to be commended for choosing what you consider quality themes to review and resell on your site. You have my best wishes in your venture.
5. You're quite right; Weblog Tools Collection does have affiliate links on it; they're located on the sidebar. None of the posted reviews have affiliate links.
How would you feel if you opened a store and someone came in and set up a booth to promote/sell their merchandise to your patrons?
I don't mean to sound capitalistic or mercenary, but the proper course of action might be for you to purchase an advertising spot on WLTC the same way other merchants and resellers do. That decision is up to you.
Again, you have my best wishes and regards.