If I were you, I would take rate from few pages (for example 5 APIs or more) and if any price is different for more than n% (n could be various - about 5%), then don't use that rate in your calculation. Or calculate statistical model (again from a few APIs) and don't use rates that has too high deviation.
Edit: now I see that this is for exchange. So why you then need ticker? Just take rates from your exchange.
I'll be using the ticker to determine the prices for the exchange. It doesn't exist at the moment so I have to use blockchain to debug on all coins LOL.