ANY appraisal is ALWAYS only an estimate, a GUESS really, and numerous appraisers will always come up with different numbers unless they're "colluding" together. And keep in mind that EVERY property is unique, and different buyers may be seeing different things about the property that appeal to them. In a volatile sellers market, it can become nearly impossible to "guess" what the highest bidder might be willing to go to.
The only REAL appraisal of value is when you put it on the market, and a buyer that wants it shows up and makes a serious offer with earnest money on the line. It's always "only worth/is worth as much as" what someone is willing to pay for it.
Some buyers will be willing to pay more than other buyers obviously... so right there you have several actual "honest appraisals" from "serious buyers" that would be willing to put their money on the line... but their opinions of what it's value is varies between them. Every auction proves this out. A good number of people go away shaking their head saying it's going too high, and they're not willing to pay that much for it, and someone goes away agreeing to pay what the sale price was.
When it's put up for sale, if you ask too little, you'll never know then what the market MIGHT have been willing to pay. If you ask too much, they can counter offer, but if you put your "ask" too high, you might also just be chasing away potential real offers that might otherwise have been made somewhat under your ask price, because they don't want to insult you with their offer, ...they may feel that you're just completely unrealistic in your ask and you're trying to take advantage of them, and so then they just don't want to deal with you,... or they may feel they'd have no chance at being accepted so they won't even try.
Remember that at an auction, alot of times, the "first bidder" starts out the process with a very unrealistic low-ball offer, but by the end of the "negotiations", they end up going home with the item at a MUCH higher price. He WAS a serious buyer, willing to go much higher............. but he also wasn't willing to make that high offer right up front, in case he would be able to get it for less.