Sounds suspicous. To start with--what types of petitions or applications? There are some types of benefits (asylum, I-601 waivers) with a comparatively low approval rate. But if you mean that 67% of all types of applications or petitions filed pro se are denied, there is no way that is true.
I doubt it is on CIS's website, they are not likely to try to broadcast that information. However we do have statistics from removal proceedings and there the evidence shows a stunning difference in approval rates between those who are represented and those who are not. Many applications, like waivers, are very hard for laymen to understand and do correctly.
The above is intended only as general information, and does not constitute legal advice. You must speak with an attorney to discuss your individual case.