I thoroughly understand the frustration of trying to guess what the reserve is on an auction. I use it only to get the buy-it-now option to stay available for a while. What I've discovered is that in auctions with buy-it-now, after the first bid is made, the buy-it-now disappears! Maybe ebay has changed this, I haven't checked lately. But, I discovered that having a reserve will keep the buy-it-now option available until the reserve is met. I haven't used many reserves, but when I do, I set it at about 75% of what I think it should go for.
One of the things I wrestle with putting items up on ebay is what price to set as a buy-it-now. When I put something up on ebay, my goal is to get it sold over getting 'top dollar'. Put another way...I want it GONE as soon as possible. So, once I've figured out what the item should typically fetch, if I really want it GONE, I'll set the buy-it-now at about 90% of that price...sometimes even lower.
It's different if you're trying to make money using ebay vs getting rid of stuff I don't want any more. Perhaps 12 years ago already, I discovered I could buy individual items on ebay, group them together and make about 10-15% in the process. It was a far cry from making a living kind of money, but it was some easy income.
These days, it's considerably more difficult to 'make a living' on ebay because the expenses have risen dramatically. Newbies to ebay selling forget how big of a 'bite' they take. In particular, ebay takes 10% or more of your sale price + shipping charges! 'Back when', people would sell $100 computer CPUs for $20 + $80 shipping, as ebay didn't take a cut of the shipping charges listed in the auction. It didn't take them long to figure out they (ebay) were getting screwed, so now they take almost nothing to list an item, and hit you for 10% of the final amount you'll be receiving. Then Paypal takes their cut...another 2-4%. I haven't taken the time to figure out exactly what percent they take as I don't sell more than 15-20 items per year. Another big cut is the actual shipping cost you pay. Don't forget that packaging materials, if you have to buy them, are part of your costs. Shipping tape is my biggest expense. I buy cheap stuff at Walmart or Staples. I get enough boxes from Amazon that I could ship just about anything I can carry. But shipping company charges get worse by the year. I sometimes figure out in advance what package and carrier I will use when the item sells. But as anyone knows, shipping cross-country is more expensive than only a couple of states away. Living in New England, I've found a good share of my buyers live on the West Coast. Go figure. Twice in the past year, I privately emailed West Coast sellers whose item(s) I had just bought if he thought that a big number of his buyers were on the East Coast. Yep! So now, I 'price' various shipping costs to Denver and hope I don't get a California buyer. Unfortunately, I did that about a year ago when I sold my pedal steel guitar on ebay and got...you guessed it!...a California buyer! I had a $100 shipping charge in the ebay listing, but it came to $135 to ship it with insurance. When possible, I've found USPS 'flat rate' boxes usually the least costly to ship, especially as items get heavier (like lenses). And even though ebay offers both USPS and Fedex shipping options, finding a Fedex place to drop off something too big for one of their drop boxes gets more difficult every year...and I'm a former Fedex Ground owner-operator and later on, employee (for the insurance). So, for me, it's either USPS or UPS...sorry Fedex.