What you have to trust
Every fill is sealed with a hash the moment it lands, and you can recompute that hash yourself. That is the part you do not have to take on trust. Here is the part you do.
The seal covers the fill, not the price it was given
A seal proves a recorded trade has not been altered since it was recorded. It cannot prove the price was right in the first place. What makes that checkable is separate: the reserves a fill was priced from are recorded with it, so the arithmetic can be repeated afterwards and a wrong fill can be caught. Caught after the fact, not prevented in advance.
Prices are read by us
The prices are real and they come from the same pools everybody else trades against. But we are the ones reading them, and a bad read is possible. Two things reduce it: the reserves behind every fill are stored, and a watchdog compares what the engine believes against what the market says and suspends trading when they diverge.
The balances are ours
Your practice balance lives in our database. There is no version of it you hold. If this server lost its data tomorrow, your record would be gone with it, and the honest answer is that snapshots are the only thing standing between you and that.
Nobody outside has reviewed this
The engine has been reviewed by the person who wrote it and by nobody else. No outside audit, no fuzzing, no formal analysis. The source is public, which is not the same thing as having been read.
Display names
Names on the leaderboard are moderated by us. Removing one changes no record and no balance, which is precisely why moderating them is safe to do.