No. 1 - Starling Marte Trade
When Cherington took over as the team's GM Starling Marte was the best player on the Pirate roster. Marte was coming off a 2019 season is which he hit for a .295/.342/.503 slash line with a 118 wRC+ and a .208 ISO.
Marte was an established star at this point in his career. He had won multiple Gold Glove Awards and had already put together 2.5 strong seasons post-PED suspension, squashing any concerns about his ability to still produce after the suspension. Marte also came with two years of team control.
Cherington should have been able to net a huge return for Marte. What he got in return for him has been anyhting but that. In exchange for Marte, Cherington landed pitcher Brennan Malone and shortstop Liover Peguero from the Arizona Diamondbacks.
Malone's career has been wrecked by injuries. Since joining the Pirate organization he has pitched just 19 innings. 14 innings in 2021, 5 innings last season, and he has not pitched yet this season. At this point, Malone is well into non-prospect territory.
As for Peguero, he has always struggled defensively at shortstop. For much of his minor league career he has also struggled offensively. This season, however, Peguero is putting together his best offensive season since 2019 hitting for a .269/.337/.445 slash line and a 110 wRC+ at Double-A. Peguero got a cup of coffee in the majors with the Pirates last season.
Peguero could still somewhat salvage this trade, but his ceiling in the majors looks to be as a utility player. Even if Peguero pans out as a utiliy guy, you should net much more than that in return for a player who was in the position Marte was in when he was traded.