The Creationist literature points out that radioactive dating techniques are based on several assumptions. Between this, and the scientific rebuttals, there gets to be quite a lot to say.
However, there is an easier way to check if a method is reliable. We can see if it gives consistent answers against some other method.
For example, Potassium-Argon (K-Ar) dating was tested against the Cenozoic-Era North American Land Mammal ordering. By ordering, I mean that rock layers were given numbers, with bigger numbers at greater depth. Each fossil was given the number of the rock layer it was found in. (Geologists call this stratigraphic order.) Here are the results:
Stratigraphic K-Ar Date # Samples Position Name of Age (millions) Dated ======== ============ ========= ========== 1 Irvingtonian 1.36 1 2 Blancan 1.5 - 3.5 7 3 Hemphillian 4.1 -10.0 8 4 Claredonian 8.9 -11.7 16 5 Barstovian 12.3-15.6 9 6 Hemingfordian 17.1 1 7 Arikareean 21.3-25.6 4 8 Orellian --- 0 9 Chadronian 31.6-37.5 9 10 Duchesnean 37.5 3 11 Uintan 42.7-45.0 2 12 Bridgerian 45.4-49.0 2 13 Wasatchian 49.2 1 14 Puercan 64.8 1The standard geological idea is that "deeper is older". (It's called the Principle of Superposition, and was invented two centuries before Darwin.) In this table, Superposition and K-Ar dating are mutually consistent.
The above is one example from
A response to creationist criticisms on radiometric dating, G. Brent Dalrymple, USGS Open-File Report #86-110, United States Geological Survey, 1986.but if the subject interests you, it is much easier to obtain his book, The Age Of The Earth.