Carbon dating - is it 100% true or based on 'faith'?

Ok, many believe the earth was formed over millions of years? Many claim this is based on solid evidence and not on 'faith' or trust about what their Science teacher told them? I say, can you back up that position - or do you simply believe what others tell you? Consider this:

1. For carbon dating to be accurate, you must assume the rate of carbon decay is constant. But changing the environment has shown the opposite to be true, and samples from various sources have also shown inaccuracies. Or do you faith that environments have never changed?

2. For carbon dating to be accurate, the ratio of carbon 12 to carbon 14 has to remain the same - as this is what is based on. But events in the earth's history such as the industrial revolution etc. have been proven to lead to a higher concentration of carbon in the earth's atmosphere (and throwing out the ratio). This is just one event out of thousands of years which could lead to a variance. Or do you have 'faith' that carbon concentrations have always been stable and vast climate/environmental changes never happened?

3. Many claim that all plant and animal life utilize carbon 14 as equally as carbon 12. But this isn't necessarily so. Live molluscs off the coast of Hawaii had their shells carbon-dated, showing that their shells died 2000 years ago! It was quite a shock to the molluscs that had been using the shells recently. Or is this report just made up?

Most evolutionists who are genuine would conclude that carbon dating is only accurate to about 3000-4000 years, as there are too many variations in non-compliant dates in carbon testing. So, to me carbon dating seems to be mostly based on ''faith' - that rules about carbon have remained true. Nobody was there millions of years ago so you cannot 'prove' carbon-dating 100% as many claim to do.