It's always a big question when we do presentations or publish journal articles as to how many decimal places we should include in the tables. I didn't get the concern about credibility though. It's more a matter of presentation. What is the ideal number of decimal places to include for your audience? If we are presenting to other scientists, it's not a concern as they can round off anyway they please. If we are presenting to a more casual audience, then we usually use fewer decimal places, so they can read it more easily. I never really thought about how too many decimal places would make you less credible.