Bias points

[mozz]

Valvehead, where are you located at? I have a few hundred of these, will put 2 in a envelope for you.

[pdf64]

Never give the customer a chance to do it wrong, because he always will

Yes, some definitely.
When my friend was using my Fender 75 head, every time he set it up, the speaker plug would get plugged into the wrong socket - ext speaker / line out / fx loop.
I eventually had to gaffa tape over all them, leaving only the main speaker socket available.

[potatofarmer]

Trace Elliot used to use XLR jacks for speaker connections. More robust than 1/4" jacks, okay, sure; but an inexperienced sound guy looking at the back of an amp he's never seen before, trying to find the DI out...

[Old Tele man]

Never give the customer a chance to do it wrong, because he always will. [snip]

Yep, because "...with a 50/50-chance, they can screw it up three times...in a row."