The Roman Catholic Church claims that some corpses have supernaturally slow decomposition. Were those bodies examined by skeptics?
Yes, some of those bodies were examined by skeptics. Io and behold:
Sometimes the saints had been mummified by skilled preparators, sometimes natural conditions significantly slowed decay. Sometimes, the corpse was just replaced again and again with a newly deceased one.
The article above concludes with:
Since we know that both natural and artificial mummification exist, so the burden of proof lies with anyone who claims that it was the work of god.