Why buy any price guide? You can search Heritage's Auction Archives and get most of the price guides for free, including Greysheet, CPG Retail, NGC, and PCGS. Furthermore, they are only guides. In your example of the 1969-S Jefferson Nickel in MS66, you rightly analyzed that all of the price guides are extremely inflated and that current auction prices are a mere fraction of the price guides. If you know that, then you price your coin accordingly and ignore the price guide.
Unfortunately, I wish that I could say that 100% of the time. All I can say is that I've had my share of stupid mistakes.
I agree with you on that one. Currently my selling price would be about $30-40 due to the simply fact that nobody got it right with pricing. Those MS66 coins are really nice examples, but sometimes it's best to price coins near their real life prices. I've seen where people pay either way below or way above any price guide. Hey, that's how we learn. I've made a fair share of mistakes as well, but when you do, it's best to learn from them and move on. Most of them were made during late 2022 to early 2023 (my early era of collecting) but I still make them today. All I can say is that it's okay to make a mistake in coins from time to time. I've learned here at CT that there are also a lot more people that believe in my coin collecting than just people I know.
I use an average of final auction prices but I'm only selling at auction. I use that same figure for insurance value for shipping. I have sold a few hundred coins on Great Collections the last few months. Most of the time my prices are really close to what they end up selling for. This makes me think that many collectors are looking at auction prices as well. I'm not very close with coins that have very little recent auction history and my guesses are all over the place. Scarce and rare variety coins are tough to guess. You need the right bidders that really want that variety. Without that the prices may not make you happy.