A long time ago I bought Technics SUV-505 amp. Absolute pants!
I also swallowed the hype on the TDL RTL3. Boom and tizz. Wish I'd known about that mod.
In more recent times, the only product I have bought that failed to impress was the Lavry DA10. The bass was pathetic. The Transporter's own DAC outperformed the Lavry so I got shot of it quick. Luckily it received so much love on a particular forum that the price was ramped up after I bought it and I was able to get back almost what I had paid.
iFi ZEN Stream/TV/CXC >> RME ADI2 DAC >> XTZ Edge A2-300 >> Rogers LS8a
PC >> Hugo 2 >> iFi Pro iCAN Sig >> Raal-Requisite CA-1a