A lot of what we price comes from experience. At one to two sales a week, you see a lot of the same things over and over, and you just put the same price on the stuff from week to week. Sometimes that changes. As I'm sure you know...something is only worth what someone is willing to pay. One time we had a sale that had over 2,000 used golf balls! We put 12 to a ziplock bag for $2.00, and sold every one! We have been charging $2.00 a dozen since then for used ones, but last weekend we had about half left over, so we put them at $1.00 a dozen this week. If they all sell, after a while...we'll put them back at $2.00 and see what happens.
As far as bigger ticket items, and antiques and collectibles...the best source really is ended auctions on ebay. If something actually sold for $250, we might put $130-$150 on it, unless it is a very rare or desireable item, then we might price it closer to it's current market value.
What a lot of the dealers and resellers that complain about estate sales fail to realize is, we are not "ebay seller wholesale supply". We are selling to the same market as they are...the final end-user/collector. The difference is...we only have 2 days to sell the stuff, so we tend to price it under current market value, and that often leaves a lot of "meat on the bones" for the dealers and resellers. It's also a business, not a hobby, so we need to make money just like they do...and we have a lot more overhead than they do....but....we are selling for a percentage, and don't have to purchase the items first like they do, so I understand that they need some room to make some money.
If there is no ended item that actually sold, and everyone is asking about the same thing, we will usually price something about 1/4 of the asking price on the auctions.
Like I said before, we usually sell about everything in the house. I would rather sell everything for cheap, than have a house full of overpriced stuff left over!
I can tell you that by conversations with dealers and resellers at our sales...that they tend to want to at least double their money. They will take a chance on some things, and will sometimes come back and tell me they did good on something, or only broke even.....
Some other advice I would give you is, be thorough. I saw a thread on here where people said if they see ebay printouts at a sale they turn around and leave! Really?! What if the ebay printout said something just like it sold for $400, and they were asking $200, and it would be half price the second day, like all the sales around here? We put out printouts sometimes to show what something is, or how valuable some, otherwise unremarkable looking, item might be, but we don't ever ask the ebay price for anything...and we are sure smart enough to know the difference between "asking" price and "selling" price. Be willing to go the extra mile and take your time. Some sellers come busting into the house, grab a few items, then run off to the next one to try to stay ahead of the other dealers. Then the other sellers come in and get all the stuff the other one overlooked!
As far as having regrets that we sold something too cheap...it happens! You just have to get over it! It bothers my mom way more than me! One guy says he got over $35k for an oil painting that he paid $65 for from us...but who knows? Another story floating around is that someone bought a painting from one of the other sales, and it had like $2,500 hidden in the back..... The way I look at it is.....if people don't make a good score every now and then, there is no reason to come to the sales unless you are looking for used furniture or something...