Don't want to go in a discussion and maybe you are completely right, but to my understanding: Miners collect the transactions on the network into large bundles

Don't want to go in a discussion and maybe you are completely right, but to my understanding: Miners collect the transactions on the network into large bundles called blocks. These blocks are strung together into one continuous, authoritative record called the block chain. Miners create blocks of transactions, and they have to create them in such a way that the rest of the network will accept them. One of the requirements is that the transactions in the block are all valid transactions. So yes, miners will validate transactions before they add the transaction to a block. If the miner cheats, and puts an invalid transaction into a block, then the rest of the network will reject that block, and the miner would have wasted their time doing the proof of work on that block. https://bitcoin.stackexchange.com/questions/148/what-exactly-is-mining https://bitcoin.stackexchange.com/questions/148/what-exactly...