Verify hash of plaintext through ciphertext
Answering in a pragmatic way (it might help, depending on the background of the question):

Even if step 3 is possible, it does not matter, since this will not add any additional security value. 

Because: Bob still has to trust Alice that she will send him K in case that he pays the money. So Bob could also simply trust Alice, that she has already send him the correct encrypted text E(M, K) in the first place.