What's up, bisnotches.
Radio-metric dating:
The parent/daughter ratios are unreliable since wether and erostion can effect. Rocks dated with this method erode, due to the elements. Any part of the rock that eroded which contained either the daughter or parent element will be incorrectly dated, either too young or too old.
There's also the fact that rocks naturally contain certain elements like Iron. That would also throw off the age of a fossil dated with this method.
Water can also wash elements into or out of rocks. Rocks dated which were found in places that at one time contained lakes or rivers which have now dried up, don't account for this when dated with radio-metric dating.
C-14:
C-14 uses the measuring the ratio of normal carbon (carbon-12) to carbon-14 in the air.
The problem is, first, that we must assume atmospheric conditions stayed relatively the same. We can't know for sure if it was the same even a thousand years ago, let alone ten, twenty or fifty thousand years ago.