Market stalls where I live (there are two retro game stalls) research the prices of games on Ebay and other various sites and whack a whopping 10% ontop. I saw Ristar in there for £35 and it didn't look that great condition. Just realised in that case it's way over 10% inflation. I suppose whoever holds the majority of the item determines the price eh. Like my Nomad has shot up like £100 in value. They're going for crazy prices.