I sell as untested cause I want a fast sell and with out having a lot of space to test items with and really have no problems since I offer a return and most things I pull to sell work already as for a store no I sell auction style because it gets more views and with that more people to contact that want special orders. I do that with my good regulars kind of like the wish list on ebay I have a updated list for different buyers so I can fill it when I come across things and know when they have gotten something already.
as for knowing prices I learned a lot over the years for some stuff to sell but mostly I just put random prices higher and lower depending so I can catch both ends of people searching as long as it sells fast and I put no more than 3 days on a auction because any longer it stalls and needs to come up right away for people on at least the first 2 pages so that it does sell fast