So as another example I just had a size 1000 WC go through the autoexchange setup at trademybit and it traded through at -20% to where the market was just before and just after the exchange from WC to BTC as done through the automated exchange setup at TMB.  Per coin value was .00000850btc as obtained by TMB's autoexchange, but the market for this coin was much higher just prior and just after this trade went through.  Perhaps the markets are super thin and the exchange crashes it, but this is a major affect on coin profitability if I mine when the coin is valued at xbtc/mh's, but the exchange system consistently gets 10-20% below the going market rate before and after the exchanges to btc are being made.

Edit: A following trade of WC as done by the autoexchange at TMB got much closer to the market rate, though here the trade was for a lot less WC.

I know I can manually do the exchange, but i'd like to see these exchange rates got for our mined coins not be consistently and in some cases substantially lower than where the market trades at just prior and just after the trade goes trough, or if this is unavoidable due to thin markets then have the value for mining the coin adjusted in some manner.