When you list an item, most of the time I would recommend an auction. This way, you know you will be getting top dollar for what you are selling. The only way I would recommend selling at a fixed price, is if you are selling a new item and you know what everyone sells them for, or if you are selling more than one thing and are pretty sure what it will sell for. Most of the time I would still recommend an auction, because when I have sold new books, my Val Kilmer biography, and even though I am selling it for the same price on an auction or a fixed price, it seems like I sell more at auction. I don't know if people like the idea of winning an item or what, this doesn't make any sense to me because as a buyer you don't have to wait if you have a buy it now, while if you are bidding on an item you would have to wait until the auction is over and you might get outbid. The only exception is when the free listings are only in a fixed format, and even then I would consider waiting for an auction. EBay usually will give you 50 free listing a month, sometimes it is for an auction and sometimes it is a fixed price listing. Currently, it is for either an auction for fixed price listings. Don't pay for listings.
Some people like to start an auction with a dollar bid, or even a penny bid. This can come back to bite you if the item isn't very popular. You can generate a lot of excitement if you start bidding at a dollar, but if you are selling something which will probably sell for $500, then the person who bids a dollar for an item isn't going to be the person who will pay $600 for your item, which is what you are trying to do when starting the bidding low. I recommend doing research to find out if your item will be popular first. Let's say that you are selling face value five dollars in junk U. S. 90% silver coins (Which are dimes, quarters, half-dollars minted 1964 and before which don't have coin collector value). That is the type of thing that will sell in a very close range and you could start a penny auction and not have the risk of selling below what the coins were worth. An 1850 Liberty Head gold coin; however, is not a good type of item to start at a dollar auction because there might not be as many bids on it. They may seem similar, but one is a commodity, the other is a specialty item. If something isn't popular, but a specialty item, list it for what you want to sell it for. If an item is a more popular item, I would recommend starting the bidding out a 60% of the value. This will create excitement but from people who might actually be willing to pay what your item is worth, or a little more. I usually do the seven-day auction. I don't think there is much difference with a ten-day auction, but it might be worth it. People who seem to be using the three or one-day auctions are selling a lot of things and are probably listing full time and can relist very easily. Every day that your item is on Ebay, it can attract attention and get a bid or have someone add it to their watchlist. Sometimes people will add items to their watchlist so that they can bid right before the auction ends.
Lastly, never, never, never, do a dollar auction with multiple items. The way that bidding works, is the lowest bid that outbids anyone else will win. So if you list twenty items at a dollar, more than twenty people would have to bid on the item before you would get more than a dollar, unless they are buying more than one item at a time.