Serious Addiction to Gear

I suggest you view the A&E show "Intervention".It broadcasts on Monday nights in most areas.It deals with many forms of addiction and destructive behavior and the effects it has on the people around them.Then the issue is dealt with by a professional and treatment is offered,usually as a last resort.Compared to some of the extreme cases i have seen it sounds like your"friend" might be a ways from hitting bottom,so it may be something he has to work out on his own.One day he might turnaround and say "what am i doing with all this crap?" And his behavior has run it's cycle.
Quite often people will ask questions like you have and refer to a "friend" in distress,while it is actually they that are seeking help.If that is the case you are not going to find the help you need on this website.I do know that there are many generous,well meaning people here that will offer support.Good luck and your friend is lucky to have someone who cares.

Can it make you blind?

Is he experiencing hallucinations, uncontrollable tremors or is he losing weight? If not, I wouldn't be alarmed.

Of course buying used audio gear can be an addiction.

It helps to move onto something healthier and less potentially addictive, like heroin and/or classy prostitutes. In fact, both at once ends up being much cheaper and less disruptive to your life than the audio thing.

Best of luck with your friend.

wait is this really for "your friend" or is this a cry for help lol?
You should see guys on Audiokarma that collect anything found at a thrift or found in a dumpster, if its cheap or free they take it no matter what!