Never Believe an amp is Beyond Repair

A number of years ago, I was once GIVEN a 1960’s top boost Vox AC30. A pint of beer had been sitting on the amp at a gig ( a No-no!). the guitarist knocked it over when he turned to adjust the amp settings. Whoosh! the beer was knocked over and poured into the amp air vents. There was  bang and the amp died. he took it to a repair shop and they told him it was beyond repair and only fit for parts.
I dismantled the amp expecting a real mess. it wa all sticky with the beer, so I cleaned this out. Two of the EL84 output valves had shattered. One of the speakers was blown. It was open circuit.
I sent the speaker off to be re-manufactured and the time this cost £5 which took four weeks.. I replaced the output valves, replaced four 220K resistors that were open circuit in the pre-amp section. Hey presto I had a fully working Vox AC 30. My conscious made me tell the guy, I had fixed the amp and he had already bought another AC30, so he said I should keep it as long I agreed  to fix his one when it went wrong.
Now why did I ever trade that amp in?