I'll weigh in on the subject about past posting at my local betting venue.

Seems on simulcast wagers the betting was/is (story is about 2 years old) controlled by a phone/data line for each track signal.
An employee hangs up an open phone line at post time to cut off betting from that simulcast location.
Seems this employee was leaving the job and set up a pastposting scheme. He would 'accidentally' leave the phone off the hook until 7 seconds after the race ended. This gives his cronies the ability to bet via tiny tims after the race is over. Two fellas manned the monitors and two the tiny tims....punched in exactas and tris on a couple of races. Not $12 pick 6's but enough to make a nice payday.
Actually called a race wrong and lost so they did one more.
Cleared some 7m to 10m from what I was told.

From my perspective, this probably can be done. It is probably still being done.

Not a pretty picture.

For the record, I was not there when it happened and would not know the day or track.
I know a name or two of alleged participants and have it on very reliable source that it did happen.