We don’t fix currency rates and never have because of the volatile nature of cryptocurrency, where the rate of any currency can fluctuate every minute. This is why the final rate may be slightly higher or lower than expected at the end of a transaction.
Keeping the rates fixed would require us to cover market risks and currency volatility, which as a result would make our commission fee much higher. Instead, Coinsnex charges a quite low commission fee (<0.5%) and offers the best available rate at the moment the transaction is completed.