If I send some bitcoins to some address, and I pay the proper fees, how sure am I that it will be included in the next block? Are there any guarantees if I want my payment to be included in the next block that is mined?
It will be included in one of the next blocks. Miners do not make profit out of stopping your transactions, they make them by creating the blocks. If one miner would filter your transaction another miner would include them, that's the nature of decentralized systems.