You do not need demonstrated prior experience or any special qualification to join, it is desirable but not necessary.
However, there are few things you need to have to become a great transcriptionist
You have very strong language skills, you love grammar and cannot tolerate typos or misspellings.
You have great attention to detail and you are able to spot even the tiniest mistakes in a text.
You are curious and you are willing to use your research skills to find more information about the vocabulary or speakers in your file.
You are patient!
You can learn the style guidelines and apply them to your work.