Virustotal is not a scanning service; it's a meta-service, allowing you to see what other scanning engines make of a file.
As such it's totally accurate in telling you what other virus scanners think of a file, but that doesn't mean the virus scanners themselves are accurate. In fact that's why services like this are useful: because a single virus scanner isn't generally very accurate, you can get a better picture by looking at what all the major scanners say together.
If they all agree a file is problematic, and especially if they all give it a similar name, then you've probably got a well-known virus. If only a few of them reckon the file's bad, and they're detecting it with woolly heuristics and generic “we don't really know what this does” names like Delf, Small, Troj and so on, then they're just as likely false positive.
(However, in the sorry condition that is today's AV environment, even when the majority of AVs agree a file is clean or not-clean, they can still very easily be wrong.)