I have bought many p-books and other items from Powell's. I bought books from them almost exclusively during the Free Software Foundation's Amazon boycott. I had occasion to return or exchange an item a number of times, but I can only remember having any sort of dispute with their customer service once.
If you are ever in Portland, Powell's City of Books is an amazing brick-and-mortar store that occupies four floors of an entire city block. I have been there often and don't recall ever having a complaint about their customer service. Well, one of their clerks yawned once when I told her how great the store was.
I wouldn't hesitate to buy a Glo from Powell's.