What has been your costliest mistake in this hobby?

My biggest mistake was to buy to IsoAcoustics Gaia I with 220 lb limit. Although provided with a kit of different mounts, non was oassing to my speakers. On top a month later I got an attractive offer and upgraded my speakers to new ones with 400+ lb of weight. Now the beautifully built IsoAcoustics still stay at home in their nice exspensive boxes...

Years after the factory had shuttered, I was swapping out a PC to my beloved Kinergetics KBA 75. Either I plugged the new PC into the wall first, or neglected to shut the amp off... sparks flew amp blown, too costly to repair

I asked Stereo Fixers in Boca Raton and Music Technology in VA to "fix" the channel imbalance in my Luxman CL-32 pre-amp.  They BOTH charged me a ton of money and "couldn't fix the problem."

When I had my shop, if we could NOT fix something, we charged the customer the $20.00 "look-at" fee and nothing else.

I guess times have changed with shops now charging lots of money for what they CAN NOT do.

If I took my car to a shop and they could not fix it, I would never pay them, nor would they charge me other than a minimum "look-at" fee in my experience.  

Cheers!

Lol great idea for a thread!

For me, impulsively buying speakers before I realized that I shouldn't be "collecting" them.  

Back in the day, bought a PS Audio 200C, money thrown away.