To be fair, the probability that the short explanation "He received money from Libya for his presidential campaign" is actually the truth is very high.
There is no formal proofs, but as you say, (the judges deliberated that) there is enough "converging indications" to support the idea that the short explanation is true.
I'm sure the court could have gotten him on other charges, but they went with the absolutely 100% safe one rather than the other 99% safe ones.
Sarkozy and all of his billionaire media allies are already trying their hardest to undermine the credibility of the justice system at every turn with extremely dangerous rhetoric; I dread to imagine what this would have been like had they gone with ever-so-slightly-less-safe charges
The short answer is you can't. But There is enough hints that he maybe implicated at least as much as his collaborators.
One for example, is a testimony of a "smuggler" that he deposited the dirty money 2 times to his collaborator and once directly to Sarkozy. Not enough, he could lie.
A write-up of a meeting preparing the coming of Sarkozy (in arabic) that suggests there is another important subject to the visit of Sarkozy in Lybia. In a way that coincides, we know that the discuss alone (Gaddafy, Sarkozy and Guéant without any diplomatic representative only translators).
Not enough, maybe it was another secret subject.
That may explains the famous trip of Gaddafy in Paris. (10 of December 2007, which was an unexpected move regarding his implication in multiple "plane terrorist attacks" (DC10 UTA ( UTA 772),Pan Am Flight 103 (Lockerbie)) and the "greatness" of the trip which was in "great fanfare" very uncommon one. https://abcnews.go.com/International/story?id=3984020
Maybe Sarkozy really trade welcoming trip for good contracts but nobody trusts that.
It can also explains the implication of Sarkozy in nato air strike on Lybia to help the rebels (that leads to Gaddafy death). Gaddafy may have ask for help to interfere the revolt, and Sarkozy couln't politicaly explains it so did the opposite. At that moment, Lybia official reported that he must get the money back and that he was financed by their money (one of the two who reported it is dead, the other one is in exile and it's more complicated because he first support Sarkozy to get extracted from Lybia as he was caught by the rebels). At that time, nobody trusted the Lybia representative as the regime was a terrorist state.
Sooo, you can't tell that he knows, but it does explains a lot.
There is no formal proofs, but as you say, (the judges deliberated that) there is enough "converging indications" to support the idea that the short explanation is true.