what would be better (and they would be more inclined to do) is make it 1M silver be 1 gold. easy way for you to burn that mountain of silver you have, and you can get the trade after every 3 battles, at least in my case. they wont want to do 1m for 200, as 500 gold is 1m silver, and 500 gold is 5 bucks. they would not be inclined to make you less inclined to buy gold with money.