In market gold rings good for high-flier (7)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

In market, gold rings good for high-flier [O (=ring, pictorially) in AU (=gold, i.e. chemical formula)] in SELL (=(to) market, trade); as a bird, a seagull could be described as a high-flier!