the many meanings of pièce, bad, good or otherwise: https://www.linguee.com/french-english/translation/pi%C3%A8ce.html
I think fake translates better as "fausse" : "C'est une fausse pièce."
" Pièce " has lots of meanings. A bad theater play (pièce de théâtre) would make sense here. It could also be a bad mechanical part.