I've forgot my only one buyer remorse. Not the kind of remorse we're discussing here, maybe - but remorse nonetheless.
I bought a used Splawn Nitro, drove hundreds km to get it, paid cash and didn't do my homeworks good enough while testing it.
The amp had big auto oscillation problems once the volume was up enough, I didn't spot it at his place. While there, testing it at home volume it had a small feedback moment but I thought was just a normal feedback for an high gain amp like that. That was my mistake: I made assumptions while I should have test it deeper. Lesson Learned.
The amp also had an half/faulty switch on it's pedal, somenthing the seller didn't mention, that motherfucker.
First time I turned the amp volume up, at band rehearsals, it was feedback hell. Unusable. And the pedal, after few stomps, started acting up....motherfucker.
The seller screwed me big time, he knew it, I'm sure he did.
Tried to get money back but the seller refused to even talk about it. He told me "you tried it, you liked it".
Brought it to a good tech and he told me that spotting the issue takes time and time is not cheap.
Sold the amp as broken loosing a lot of money.