Paper doesn't help
Paper trails don't really help.
If the machine prints out a receipt saying that you voted for Candidate A (which is in itself a bad thing; imagine this on a company notice board: "All employees who wish to take time out of work to go to vote must show a valid receipt showing that they for the factory owner's brother-in-law, under penalty of dismissal"), then nothing is stopping it from recording a vote for Candidate B.
In fact, it doesn't even matter what the machines record. A really corrupt election administration could just make up any numbers they wanted, and you'd have no way to verify it.
Suppose Candidate A receives 500 votes, B receives 390 and C receives 110. These are the *actual* votes, remember. The *announced* result, however, is: A 380, B 500, C 120. (Note that those figures are not so far out as to be utterly implausible. If they wanted to get a candidate elected in the face of very strong opposition, they might have to field a few extra candidates of their own just in order to split the vote.) You voted for A. You go with your receipt to the Town Hall to check how your vote was recorded, and are correctly told you voted for A. And that’s as far as you can take the matter.
Even if all 499 of the other people who voted for A go and check, they’ll be told — rightly — that their vote was for A. And because (1) they all go in one at a time to check their vote, and (2) there are also many B- and C-voters in there, not one single one of the A-voters will be the slightest bit the wiser that there are really 500 of them, as opposed to the 380 that was announced!
You could only ever determine that something was amiss if all those A-voters produced their receipts for Candidate A *at the same time*. And a lot of those receipts will have been lost or destroyed.
At least if the counting is done manually by the actual candidates themselves and their representatives, we can be sure that it's correct; because as long as none of them trust any of the others, the only result they can ever agree on is the truth.