This is the single most common heartbreak in automated trading, and it’s rarely because the EA is “fake”.
The usual culprits, in order: (1) the backtest used poor tick data or a 90% model instead of every-tick 99.9%; (2) spread and slippage on the live account are wider than the test assumed; (3) the parameters were curve-fit to the past — a profit factor above ~2.5 over many years is a red flag, not a selling point; (4) the live broker’s leverage/feed differs from the test.
The defense I trust: out-of-sample testing (optimize on the first half, validate on the untouched second half) and treating suspiciously perfect numbers with suspicion. What’s the biggest backtest-vs-live gap you’ve personally hit?