Civil society organisations Transparency International Ukraine, Automaidan, Anti-Corruption Action Center and Dejure stated that Kostin did not satisfy the integrity criteria of the competition.

In 2021, a commission was established to interview candidates for the head of the Ukrainian Specialized Anti-Corruption Prosecutor's Office (SAPO), a key position for resolving corruption in Ukraine.

In 2019, Kostin sold two flats in Odesa for a total of ₴1.2 million without reporting the sale to the National Agency for Prevention of Corruption (NAPC).

[9] Olena Shcherban, a lawyer of the Anti-Corruption Action Center, stated that Kostin should have been ineligible under the criteria for political neutrality, since he was a member of the Servant of the People party and was the head of the Verkhovna Rada legal policy committee.

[12] On 27 July 2022, Kostin was voted by the Verkhovna Rada, the Ukrainian parliament, as the new Prosecutor General of Ukraine, in replacement of Iryna Venediktova.

[3][6] On 3 November 2022, Kostin, refused to open a case against his former party colleague Iryna Allakhverdiyeva for receiving a gift of ₴20 million within the prescribed period.

Following the 2022 Russian invasion of Ukraine dozens of Ukrainian officials are alleged to have abused their position to avoided military service by having received false disability status declarations.