I get to hang out with musicians somewhat often, am super lucky to even have become friends with some famous bands over the past 15+ years, and have been building up quite the collection of autographed stuff on the side. A majority of posters are either one or two of a kind since I photoshop them myself. If they're two of a kind, it's only because I'm keeping one for my personal collection. I will always specify.
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I got bit by the bug to start selling stuff after I had a very major craniectomy, a brain infection, surgeries, followed by seizures as a side effect. I couldn't go back to my regular job, which was a tattoo artist, because I get intense vertigo if I lean forward amongst a list of other crappy physical side effects. Autographs really brightened me up while I was going through dark times, confined to my bed and house for a year, but now I'm up for selling stuff here and there. I'm a collector, but it would be nice to make a couple of bucks.
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I guarantee that everything is authentic. I take pictures with people that I get autographs from, and provide as much proof as I can. That being said, I feel weird if I hold up a bunch of stuff next to the person for a picture, like I'm just there for profit, so I don't always have those kind of photos available. But, I'm willing to, and even much prefer to, get whatever item authenticated by one of the trusted companies for your peace of mind. My reputation is everything to me, in both the metal community and this one, so I even show my face in posts without worry.