From the other perspective as a seller, you have to add 20% to your bottom number as your minimum, to cover eBay and PayPal fees.
then you need to add a bit of “meat” which can be trimmed back to your minimum, so the buyer can get a “discount”, unless you run an auction with either you minimum set, or starting at your minimum.
(as a buyer I avoid reserve auctions as I’ve been at the top with a fair offers and seller doesn’t sell. Then the item is relisted at an even higher buy point. Basically trying to inflate the market with a single data point. I don’t even entertain those now, and I also don’t sell with a reserve ever. )
Then, since eBay is the new blue book, everyone outside eBay assumes the asking price is the selling price. So the average gets driven up, even without justification. How many times have you heard “even higher on eBay” or “one just sold on eBay for more” at tag sales etc. “this isn’t eBay.”...
Everything “used to” be obscure, so there wasn’t 13 sellers with Akai tape decks. Therefore you could ask, and maybe get, because there was no reference- supply and demand. But, now any old gear can be had pretty easily, so buyers have choices usually, but at the higher average selling price.