USDT to VND

No. It is an indicative rate, which tells you roughly what an amount is worth right now. An actual purchase or sale is quoted separately at the moment you commit, and that quote includes the spread. Treat this figure as a reference point rather than an offer.

Frequently enough to be useful, and never often enough to be exact. Crypto markets run continuously, so any displayed number is already slightly behind the market by the time you read it. On a calm day the difference is negligible; during a sharp move it is not.

Because there is no single price. Each site averages a different set of venues, weights them differently, and updates on its own schedule. Two accurate sources can disagree by a fraction of a percent at any instant, and by more than that when the market is moving quickly.

The difference between what you can buy at and what you can sell at. It exists on every market, not only crypto, and it is how the venue earns its margin. Deep pairs carry small spreads. Thin ones carry wider spreads, sometimes considerably wider.

For ordinary amounts, barely. For large ones, yes. A big order works its way down the order book and the average price it achieves is worse than the price at the top of it. This is why sizeable conversions are usually split into smaller pieces rather than executed at once.

Yes. Every pair here works in both directions. Use the swap control to see the same market from the other side; the rate is not the exact inverse, because the spread applies whichever way you are going.

No. Rates are shown to anyone. An account is only needed when you want to actually buy or sell, at which point identity verification applies before any money moves.

The market keeps moving. Providers hold a quoted rate for a short fixed window so you are not chasing a number that changes as you type, and re-quote once it lapses. If a payment takes longer than that window, the rate is refreshed rather than honoured indefinitely.