How is the rate locked when exchanging altcoins for cash?

The payout amount to the client in the order is locked, provided the rate changes by no more than 0.3% before the transaction is completed.
Otherwise, the payout amount may be recalculated at the current site rate, or a refund may be issued under the site's rules.
The rate in the order is built from the formula: cryptocurrency-to-USDT rate on Binance × the ruble rate on Forex — % fee.
We want our clients to be happy with every exchange they make with us, so we recalculate very rarely — for example, if the cryptocurrency rate drops sharply and significantly. In that case we will provide a screenshot showing that the rate has indeed fallen, so that the client can see the truth of our words for themselves.