Miners are reliable as far as:

1- Provably, they are not inflating the supply of bitcoins by breaching the regulations built into the protocol.

2- There is proof that any incoming fund to a wallet approved by miners, comes with an equal deduction from the ledger maintained by them.

3- There is a safe threshold for the number of confirmations where the costs of rewriting the blockchain outperform any criminal incentive for defrauding users by orders of magnitude.