Recently eBay ran a promotion where I was able to post as many auction style listings as I wanted for a week, so I got a good taste of the auction format. I think that we all think of the word "auction" and imagine getting several bids on an item, but the truth is that for most of my auction items, I only get one bid. I think this is pretty common--and it can even happen for "popular" items because there are just so many items out there. I learned this within the first couple weeks of starting on eBay, so I'm careful with what I set as the opening bid for an auction and make sure to choose a price where I'm fine with the price being the one and only bid (in other words, the sale price). Of course I do sometimes get lucky and see a little bidding war happen for an item, but that's a lucky thing, not an everyday situation for me at this point.
A nice aspect of the fixed price format is that you can also check a little box which says you'll allow customers to message you with their "best offers" for your items; a lot of sellers recommend this because it gives people a sense of control over the price they're paying. So if you list a fixed price item, you can strategize about your pricing so that you're pricing the item at a fair price but also a price where you'd be OK with taking a little less than what's listed. Now eBay has offered me a promotion to list a bunch of fixed price items without a listing fee, so I'll be doing a lot of fixed price listings over the next week. I'm never sure what duration to set these listings for; I usually choose 30 days, but I think I'll try different time periods.
Any preference for auction vs. fixed price?