After winning a coin in a Holy Land auction and sending three emails requesting an invoice over a month long period, I contacted Simon Wieland and Sandro Kopp at biddr and said I wanted to file a complaint against Holy Land and its owner Maxim Shick. I explained that I realized that biddr had no control over the auction houses that it supports on its site, but that an auction house that grew a bad reputation would also taint biddr's own reputation. After one day I received this explanation from Simon. It seems that Holy Land had answered all of my emails, but for some reason I was not receiving them, and Maxim had contacted biddr about this problem himself. Sandro also tried contacting me about the email problem but received no response from me because his email did not get through either. Now here's the good part. I had mentioned Coin Talk in my email to biddr, so Simon took it upon himself to locate me at Coin Talk. He sent me an email through my Coin Talk account hoping it would get through with an explanation about all that had happened. Well, it did get through and I responded to Holy Land and biddr using a different email address. My coin has been paid for and is on its way to me thanks to the concern and perseverance of Simon Wieland at biddr. I am not sure why I was not receiving those emails, but I will certainly be aware of a possible problem should it reoccur.
Thank you very much @tartanhill and @Severus Alexander for your kind words. People usually tend to share only their negative experiences, so I am very happy to read some positive feedback for a change!
A good lesson here. When possible, provide an alternate means of contact. A (free) Google Voice number has been very helpful to me, because t-mobile is often on the blink (lost calls and texts) and I haven't had a landline in twenty years. So people who know me well text me there (GV) when I seem unresponsive.