My worst involves trading my Pedulla MVP - a fantastic bass - for a Wal Custom in Music Ground. Got £475 for the Pedulla against £895 for the Wal. Unfortunately I found the Wal nowhere near as good live as the Pedulla (IMO) and soon after (‘96-ish?) I sold it to a friend for £550, IIRC.
That’s bad enough, but with the money I bought a Marshall Dynamic 200w bass head and 1x15 cab, which turned out to be pants. 🙄 I then swapped those for a Marshall Superbass (which was great actually) and matching 4x12 (which wasn’t), later selling them for a combined £250. So in effect I let my Wal Custom go for £250, as if £550 wasn’t bad enough!
Luckily my friend loved the Wal Custom and so far as I’m aware still has it. I much preferred the Pro if I’m honest, although I’d be interested to try the Custom again as there’s been a lot of water (and basses) under the bridge since ‘96!