In 95/96???.. I bought a PCGS MS63 1857-S gold dollar. At the time it was the only coin graded MS63 and none higher, even to this day there are only 2 graded 63, one graded 64, none higher.Even after 20 yrs I still regret selling that coin.
10 years ago. it was my first expensive coin of 2 payments totalling $375.00 a San Marino 1986 5 escudos bee 1/2 ounce gold coin. had to sell it because of hard times. do i regret it ? yes. I got $900.00 for it. only 7,000 minted. i am sure i can buy another 1 but finding them is a problem sometimes. it's either 1 comes on the market and then i have no money or have the money and no coin can be found. then i buy other coins.
Back in the 70's I bought an 1893-S Morgan -- raw of course. I bought as VG. When I finally got around to slabbing it (late 90's?) it came back G-06 from PCGS. Close enough. Since my Morgan collection was 90% raw I decided to sell but keep the keys. But I saw a 1790's something that I wanted for my type set so I used the Morgan for trade. Probably got something in the $1800-1900 range for it (other coins involved). I like the coin I traded for but I think I'd like to still have that Morgan. Did about the same thing with an 1894 Morgan (VF-35 PCGS).
My top finds so far are a 1914 $2 1/2 I bought raw that graded MS63, and a 1911 $2 1/2 I bought raw that graded AU55 weak D. Both bought for a couple hundred, both worth a couple thousand. Do not regret selling them. It scares me to have too much money in one coin!
Sold an 1879 GSA (ungraded...probably 63) for $6750. I then bought it for $5800 and delivered it to my buyer. No regrets whatsoever.
A gorgeous lightly toned 1873-CC N/A 50c . . . I bought it around 1990, got it graded AU58 by PCGS, and was very disappointed I didn't get the MS63 I was hoping for, or at least the MS62 I expected. After I sold it for a meager profit, it eventually found its way into a PCGS MS64 holder . . . ugh, that was a lot of milk I spilled.
Im sure we all have our regrets. Mine is actually kind of embarrassing but Ill own up to it. I bought a 1917 T1 SLQ out of a dansco type set a friend of mine had consigned to him. I paid $190 for it about 5 years ago or so. At the time, I was not a PCGS member and didn't want to look into sending it. I knew it was an extremely high grade, probably a 66+ or 67. Absolutely superbly struck coin with no flaws to the naked eye. Sold it within weeks after purchase for $400. My absolute biggest coin related regret. Makes me sad thinking about it to this day but there will always be another great find.
My biggest regret is that I quit smoking on 9/26/2014 and I still can't afford to buy any more coins. Chris