Liquidity changes through the day
The availability of buyers and sellers varies across sessions and around market events. A spread observed during an active session may not describe the conditions near a daily rollover. Review the times when a strategy normally enters and exits, and compare them with the conditions available on your own account.

Separate the quoted and filled price
A displayed quote is not a promise of execution at that exact price. Order type, available liquidity and the broker execution process can affect the fill. Record both the intended instruction and the resulting transaction so that differences can be reviewed without guessing whether the cause was timing, settings or market movement.
Compare like with like
Execution comparisons need consistent symbols, account types and observation windows. Contract specifications can differ even when symbols have similar names. Keep notes about spreads, commissions and trading hours. A single favourable transaction does not establish the typical cost of following a strategy over a longer period.
Review exceptions deliberately
Identify conditions that call for additional review, such as unusually wide spreads or repeated rejections. Test what your copy controls do in those situations and understand how pausing affects existing positions. An execution plan should cover ordinary activity and exceptions, with enough recorded evidence to investigate discrepancies later.
Continue with our guide to reading provider performance without promises.
Reference: FCA explanation of copy trading.