Juventus didn't sell Dybala, his contract ran out and he didn't want to renew so he left for Roma as a free agent. He is not going to try to prove anything to Juve, he left the club in a friendly circumstance and i know all he has for Juventus is respect, and the club respects him too, if he is going to play tomorrow, he is going out there as a professional to do the job he is paid for, it will be an emotional return for him to the place he called home, but that emotion will only be before and after the game, during the match only Roma will be on his mind.
Previously they wanted to sign a new contract with Dybala and they mostly agreed with each other. Later, when Juventus got Vlahovic, they decided to build a future plan with Vlahovic, and striked Dybala from their plan.
Dybala fell into a situation like Roberto Baggio after Juventus planned with Del Piero and no longer want to use Baggio for their long plan.
Juventus are right about the potential of Vlahovic who can improve and become one of best strikers after the generation of Ronaldo, Lewandowsky and Ibrahimovic. Dybala had to leave and Roma gave him a belief and big plan together with Moruinho efforts and reputation, the convinced Dybala to join.