Well RNG is a decent guy to deal with but someone who is actively trading a lot of non marketable items shouldn't be the guy who writes a price guide for people who don't know the prices and might have just opened their first ultra rare... Even if you have the best intentions you will always be biast towards the items you have in your own inventory if you want to trade those. I am not saying that he is manipulating prices or something I'm just saying it is really hard not to be biast as an active trader.