A trademark of creationism is the ability to create doubt in processes and evidence where doubt shouldn't exist. Take radiometric dating, there are various dating techniques that are used by scientists in order to date various materials. There's dozens of means to date, both absolute and relative, and there are trappings to the process as well. What creationists do is find one example of where dating has failed (usually involving carbon dating, which can't be used past ~50,000 years anyway) to cast unreasonable doubt on the entire enterprise of ageing the earth.
A murder scene
Imagine you are a detective for a local law-enforcement agency and you are called out to investigate a murder. The evidence is as follows: the watch of the victim is broken and stopped at 10:15pm. The temperature of the victim's body indicates the victim died between 10pm and 10:30pm. An argument was heard by the neighbours at 10:10pm, and local CCTV cameras picked up a figure leaving the victim's apartment at 10:20pm. All these factors point to the murder taking place at approximately 10:15pm right?
Now there are certain ways all evidence here could be falsified. The watch could have been running fast or broken at an earlier time. The forensic analyst could have made a mistake calculating the time of death. The argument the neighbours heard might not have been between the murderer and the victim, and they could have also had the time wrong on their clock. And while the CCTV may have been accurate, it's not proof that the murder took place at that time - it only puts movement out of the apartment around the time of the supposed murder.
Now if in court, all these facts were established to be true, could a defence lawyer argue that because at one point in time that a different watch was shown to be inaccurate (my watch is currently 2 minutes fast) that no watch is permissible? What about because a forensic analyst has botched the time of death before that any forensic analyst cannot be trusted? That because eyewitness testimony can be shown to be wrong that the neighbours aren't reliable? And because of all that, the CCTV footage showing the murderer leaving the apartment at 10:20pm cannot be placed to the time of murder?
Creationists not only play this game, but play it on an absurd level. Instead of being off by a few minutes, they are arguing that the data is wrong by a factor of almost a million. The time frame in question is a factor of 30 minutes, the creationist equivalent would put the murder in the dark ages, not long after the rise of Islam. They just aren't banking on scientists being wrong, they are banking on the scale of the error to be gargantuan.
When scientists have dated the oldest rocks and minerals found on earth and on the moon, a variety of radiometric techniques are used - all pointing to around the same time. A lunar rock for example taken on the Apollo 11 3.49 and 3.58 billion years ago. Different techniques rely on different decay rates, so for different tests to show almost identical results is testament to the power of the test. We can't verify that the rock is 3.5 billion years old through direct observation, but when multiple sources all show the same date then the confidence in the age of the rock is secured. To take one example of where dating hasn't worked (there are a few out there) and dismiss all tests on that manner is creating unreasonable doubt where there shouldn't be.
Back in court and the defence lawyer is on the attack against the prosecuting lawyer. In another case years back, the prosecuting lawyer once showed evidence that turned out to be fraudulent. From there, the defence lawyer argues that the prosecuting lawyer (even though he was unaware that the evidence was fraudulent) should never be trusted again and that any evidence presented has that same doubt over it. And she goes further too, arguing that the detective involved in the crime is distantly related to the person who initially presented the fraudulent evidence and can't be trusted either.
Fraud exists in any discipline, whether it be science, politics, finance, or even religion. It's a symptom of the frailty that is humanity, that at times certain people lie for some nefarious (or even noble) purpose. There have been cases of fraud in the history of biology, Piltdown man and Haeckel's embryo diagrams come to mind. There was also the recent case of Schön's nanotechnology and the Korean scientists who cloned a dog. Fraud does happen and it means that scientists need to be ever vigilant for deliberate acts of subversion.
What creationists do is use these and other examples (sometimes where there's no fraud at all) to cast doubt on the entire scientific enterprise. Again, it's the creation of unreasonable doubt where it need not exist. Because Piltdown man was a fraud, it does not follow that all hominan fossils are frauds. Likewise because Haekel's embryo drawings where faked, that since then scientists haven't updated their knowledge and still basing evo-devo on false assumptions. The sheer amount of evidence that all correlates again is staggering, the dismissal of all evidence based on a couple of bad examples is like arguing that because a lawyer has been shown to lie that no lawyers can be trusted, or that because of one bank ripping off customers that no bank can be trusted.
Again, no-one was there to witness the fossilisation of our would-be ancestors. But the fossils that have been found fit a pattern consistent with morphological change, that fit in with geographic predictions, that also fit in with genetic evidence. All these factors tell a consistent story much like the story of the murder above. Occasionally some things are slightly out of place, but that's not enough to dismiss all the evidence that does fit. Human knowledge is a cumulative endeavour, individually each piece may be fallible, but when hundreds then thousands of pieces all fit together then a pattern can be established and takes more than arguing against one piece in order to dismiss the pattern.
I wonder how a creationist would feel if every instance of fraud was used to dismiss their religion. How about the death warrant of Jesus, or the modified writings of Josephus. Then there's the Shroud of Turin, and the bleeding statues in churches all around the world. There's claimed miracles that simply weren't, person after person claiming to have spoke to God personally (including Pat Robertson year after year), all this and more has been either accidental or deliberate fraud done under the guise of Christianity. To take these instances of fraud as a demonstration that God isn't there would surely irk a creationist. The truth of Catholicism for example does not rest on whether the Shroud of Turin was created in the 14th century.
It's important to recognise that humans are fallible and are at times not above proving their beliefs by any means necessary, it's important to recognise that fraud happens. Because fraud happens, it means that we need to be ever-vigilant of such trickery. But it does not mean that anything even loosely associated with an instance of fraud or doubt must be cast with that same unreasonable doubt. Reasonable doubt is good, unreasonable doubt is just dismissal without consideration. To do the latter is a dangerous intellectual exercise for anyone who wants to be honest.