My parent's biggest selling decision was when they traded in the 1969 GT500 they bought brand new; traded it in for a 1970 Olds Delta 88 convertible
A few of my mistakes;
Passing on the Ivy Green '66 GT350 for $8,000 at Carlisle back in the mid eighties.
Not buying the Palladium silver RAIV Judge that was for sale at Carlisle in the early '80's. Car was a former POCI national champion and was perfect.
Not checking out the grabber blue '70 Boss 302 that was for sale at a place called "Car Village" in Pa. back in the '80's.
Finally, selling my Forrest Green '70 Z28 because I wasn't real fond of the green color (I love it now) and also selling my 1968 SS/RS 396 Camaro. Sold that one when the wife and I bought our house and we needed things.