Timbre and overtones. If he can't hear the difference then all the better for me that he'll miss the gem and I'll find the prize next time I buy a guitar. Last time I bought a guitar for myself I was in Singapore -- I went into a Tom Lee Music there and they had about 400 acoustic guitars in stock and on display. I spent 2 days playing through them, rejecting and isolating the good from bad until I had my shortlist of about 10 to 15. I'd already found my guitar at that point but I went further and paid to restring the last 10 or 12 before continuing to test and play. The next day I walked out of the shop before it closed with a guitar that was amazing. Total time spent was about 12 hours over 3 days --- I was a 24 year old kid at the time (Holy shit? The last guitar I bought was 20 years ago -- bloody hell, that shit ain't right) and the guys at Tom Lee had never seen anyone spend that kind of time to buy a guitar before. They didn't know what to make of me. I blew their minds when I bought the strings and restrung that last group (leaving them overnight). For me it was an amazing experience - to compare that many instruments virtually unmolested in a big guitar store (the acoustics had their own floor I think so nobody playing eruption or Stairway or Crazy Train). Every guitar played was a revelation as I compared them. Same makes, different makes, same models, different models. Was fully prepared to lay out the big money and buy the best guitar they had there (With only the absolute top shelf stuff like vintage Martins and Taylors really off my list as this was to be a travel guitar), and in the end, to my enormous surprise, I walked out with a humble Yamaha FG-421 for around 400 Singaporean dollars that sounded and played better than anything in the shop. This guitar has been all over the world with me, from the Himalayas to the Mekong Delta - To the moors of Devon, and the streets of Antwerp. I've handed it over to more people to play in more places wondering if I'd ever see it again - and as I sit here typing this the guitar rests beside me on my couch. The point to this is that every instrument has individual characteristics that define it. And the more you play it, the more in tune to those characteristics you become as a player - the more you are able to exploit and suppress them as necessary. The more you are able to evoke the magic and suppress the suck. Instruments are individual -- even mass produced ones. If this guy can't hear the difference that's his problem. He wont be selling me a guitar nor will he ever be touching one of mine. He can bully his way through life slapping people in the face with a bag of dicks -- I'll just keep playing my guitars.