While there were a huge number of fake relics in Medieval Europe those that survive can be shown to be clever but crude forgeries. If the shroud were a Medieval fake, why would the image defy even the most sophisticate modern analysis? In those days a crude forgery would have fooled even the most educated. There would simply be no reason in those days to create such an elaborate hoax. There have also been I believe some very compelling questions about the radio carbon analysis.
The best argument against it being medieval fraud is the fact that fooling the hoi polloi and even the sophisticates of that era did not require sophisticated fakery. Grab a large cloth, smear it with some goat's blood in the appropriate locations, hang out a shingle and start collecting the sous of the pilgrims.
Some pig knuckles could substitute for the finger bones of John the Baptist. . . rinse repeat and you have the toe of Joan d'Arc. . . and the money flows in to your coffers.