Rendo has very little to do with how and when the vendors return their emails or sitemails, all they can do is poke them a bit harder.  I do agree with you that the vendors SHOULD answer their emails/sitemails there is no argument about that and one would hope that we the customer would actually carry more clout then Rendo does.  I have also experienced a time lag from a vendor, but I just go to the store admin here and hope they can take care of it, they usually do in a quite timely manner.  It's good sometimes to have a go between, even though as you said dyraven, they should be professionals in their field by the time they reach the store and know that they need to answer their customers.

As far as where to lodge a complaint, I have found this forum and site mails to the appropriate admin or moderator usually do the trick for me.  I try to give them 24 hours to answer as they all lives away from Rendo I think.......at least I would hope so.

Marmac, I hope you get your answer from the vendor soon :)

Personally I have been a Rendo customer for a very long time, a former vendor as well.  Some of my favorite vendors sell from here and since I am an artist, there is no way I'm going to limit myself or my art by not shopping from a particular store unless I have a WAY better reason then the vendor won't answer my sitemail.