I haven't really made too many mistakes when it comes to high-end stereo equipment actually. But here goes:
1. Sony DVP-S9000ES SACE/CD player. A fair 2 channel SACD player and a mediocre, at best, CD player. (Thankfully bought used - still own it for the few SACDs that I own, but it was not good enough to get me hooked on SACD as a format.) Overall I would grade it as a C- piece.
2. Audio Research PH-3 phono preamp. A decent enough phono preamp, which worked well, but the mute switch did break. Not a very flexible unit though. I'd give it a grade C+.
3. A Nakamichi BX-2 cassette deck. Bought used for $50. Broke about the fifth time I used it. Oh well, it was only $50, so I did not expect much. I'd give this unit a grade D-. Still have it. Maybe I can fix it.