Every trade has a hidden cost beyond exchange fees: the bid-ask spread and slippage. On illiquid pairs, this hidden tax can silently eat more of your profit than the trading fee itself.
The bid is the highest price buyers will pay; the ask is the lowest price sellers will accept. The gap between them is the spread — you always buy at the ask and sell at the bid, losing the spread on a round-trip trade.
Slippage is the difference between the price you expected and the price you actually got, caused by your order size moving through the order book. Large orders on thin order books get filled at progressively worse prices.
BTC/USDT has spreads often under 0.01% with deep order books. A newly listed micro-cap altcoin can have 2-5% spreads and severe slippage on even a modest-sized order — the real cost of trading it is much higher than the fee schedule suggests.
Use limit orders on illiquid pairs instead of market orders. Break large orders into smaller chunks. Check the order book depth before entering — if your order size is a large fraction of visible liquidity, expect real slippage.
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