I regret selling my dark purple Jackson Soloist over 20 years ago. It was one of the first few guitars I had bought but one of the pickups stopped working in it, so I brought it to get repaired and the salesmen clearly knew I didn't know anything about guitars and told me the guitar wasn't repairable and offered me $100 towards another guitar, so I ended up with a Samick!
I regret selling my Triaxis and 290 to
@Brock because I took really good care of it and it was practically new but it got damaged during shipping. USPS paid for the repair but Mesa Boogie took over a month to repair it and didn't fix it the first time, so it had to go back a second time. Thankfully Brock was really patient and was able to get the Phat Mod removed during the repair, so it worked out in his favor.
I regret not buying a friends Marshall JCM 900 DSL 100 amp that had gotten damaged and needed major repair, so once it was fixed it no longer sounded like the amp but it sounded amazing. I'm sure I can get the sound in the Axe-Fx II but I wish I would have bought it as a reference.
I still have 11 7 string guitars in almost new condition that I should sell because I never use them but I 'm afraid I'll regret it and I'd have a hard time finding them again in the condition they're in. When I find something I like, I have a habit of buying 2, so I have a backup. I bought most of the guitars below as NOS in the early 2000's because they were on eBay and I was the only person that bid on them, so I sometimes won 4 guitars at once when I only wanted one
Epiphone Les Paul Classic 7 Transparent Black with EMG 707 and 781 active pickups
Epiphone Les Paul Classic 7 Transparent Black
Epiphone Les Paul Classic 7 Sunburst
Epiphone Les Paul Classic 7 Sunburst
Epiphone Korina Flying V 7 Black
Epiphone Korina Flying V 7 Black
Epiphone Korina Flying V 7 Black
Dean ML X7 Metallic Charcoal
ESP LTD H-207 Transparent Red
ESP LTD H-207 Transparent Black
Schecter Jazz 7 Sunburst - I had a red one too but I sold it to a friend who really wanted it but I haven't regretted it yet