Oliver White, 27, who was tied up and put in a headlock during the raid, took his own life the next day as a direct result, a court was told.
More than 70 high-value watches were taken from the 247 Kettles shop in Richmond on May 25 last year.
Kyle Mehmet, 40, of Rotherham, and Michael Holmes, 34, of Sheffield, were convicted of conspiracy to rob after a trial at Woolwich Crown Court.
Mannix Pedro, 37, of Woking, was found guilty of the same offence in February.
In a state of distress, Mr White tried to transfer £14,000 in savings to his bosses after the theft, prosecutors said.
Earlier this year, a trial heard he did not see “the risk or bad in anyone” and “showed real enthusiasm for his work at Kettles”.
But Mr White told his girlfriend he had been accused by a man “of not putting up enough of a fight”.
Not long after transferring the cash, he went missing and stopped replying to texts or calls. His body was found by a friend in a wooded area he visited as a child.
None of the stolen watches has been recovered and the shop had no insurance, despite being the target of a theft three years earlier.
Earlier this year, Junior Kunu, 31, of Mitcham, was cleared of conspiracy to rob the shop.
Kunu said the robbery was “staged” and everyone involved consented – including Mr White, whom he claimed would have “put up more of a fight” if he had thought the robbery was real.
Mehmet, Holmes and Pedro will be sentenced at a later date.
Anyone can call the Samaritans charity for free on 116 123, email them at jo@samaritans.org, or visit www.samaritans.org to find your nearest branch.
