Not even close, and you don't know what you're talking about.
The Martinez deal is up there on the list but not close to the worst. The Piazza deal - his contract with the Dodgers was ending, he had seven great years with them, and no one knows what the future holds for aging catchers. And they got good value for Piazza - five players. You're calling Gary Sheffield, who had 129 homers in four seasons in LA, TRASH??!!
That trade actually worked out decently for the Marlins, too. Two of the three nobodies Florida got were traded for important pieces of their 2003 World Series Champs. And the Mets got Piazza. It was nowhere near even a bad trade.
In 1996, 1997 and 1998, Mark McGwire hit 57, 58 and 70 home runs. In the midst of that 58 homer year, Oakland basically gave him to St Louis; though in their defense, he wanted out of Oaklnad badly and would probably not have made a deal to stay. The problem is that the three guys the As got for him did nothing.
Curt Schilling was involved in two bad trades. The Orioles traded the young Schilling, along with a very good hitter, Steve Finley, and another solid arm, Pete Harnisch, to Houston. Baltimore got Glenn Davis, a guy with good power but whose best days were behind him.
And then Philadelphia got nothing from Arizona. He only went on to pitch on three World Champion teams, going 4-1 with a 2.06 ERA and winning World Series MVP in 2001.