A British Horseracing Authority (BHA) panel has suspended him for six months, saying his original four-year ban was "too substantial to stand".
It found the trainer had told Paul John to stop Echo Brava and Missile Man at meetings in December 2015.
Best was banned until 2020 at a first hearing, but that verdict was quashed because of "an appearance of bias".
Best can appeal against Monday's verdict.
Matthew Lohn, the solicitor who chaired the initial hearing, was carrying out other work for the BHA at the time.
There was no suggestion that Lohn had been biased against Best, but the BHA did find the panel's reasons for its findings were "insufficient to support its decision in this case".
The new three-man disciplinary panel, chaired by Sir William Gage, found Best guilty of not giving proper instructions to John and of conduct prejudicial to horse racing.
John rode Echo Brava at Plumpton on 14 December and Missile Man at Towcester three days later. Both horses finished unplaced.
Gage said: "We find that Mr John did intentionally ride both horses other than on their merits: that is, these were 'stopping' rides.
"We also find that is overwhelmingly likely that he rode in that way because those were Mr Best's instructions."
Trainer Jim Best has been found guilty by a second disciplinary panel of ordering a jockey not to win two races.