Anything looks credible in a certain context. You need to pick something that’s already used by their established, credible, trustworthy competitors.

As James mentioned it all depends on the context.

- What kind of service does the company offer?
- Target Market?
- Message they want to convey?
- Who are the competitors?
- Why is their service better?

etc.

Get half upfront.
Sounds a bit dodgy.

:-) In a recent survey Times was regarded as a very serious typeface for political and economical contents.
I’d say take an elegant and crisp type and set it properly.

Nick is totally right! :D Get half upfront. They have to show their trustworthy business first.

Rigid but not too homogeneous, sheared wedge serif.
Like this: http://themicrofoundry.com/ad/CR.pdf

BTW, I get half up front as a rule. But the other half only
when the client is 100% satisfied. This builds trust both ways.

hhp

I want my bank to be credible and trustworthy. I want the guy who fixes my car to be credible and trustworthy too.
If my bank uses Trajan for their logo, the message I get is "credible and trustworthy." If the guy who fixes my car uses Trajan for his logo, the message I get is "expensive and slow."
As James and Jörg said, context is everything.

Yes context plays a major part, but of course it's not everything – on a deeper level there are certainly parameters that up a font's general "credibility meter", like a certain solidity/stability for example in terms of width (not too narrow), weight (not too fragile), rigidity (not wobbly), serif structure/shape (solid, not lyrical – maybe even slabs). It should make the client feel good and secure; so no surprises, no unexpected strangeness or quirks, and probably nothing aggressive (like spikiness).

But that still leaves a wide range, and these criteria will also vary depending on context; so. What does that client even do?

What she said.
Nothing is everything - everything is something.
Making context omnipotent is anathema to Design.

BTW, to some extent Trajan says "go away and let
me strike this pose" no matter the context. And in the
context of a bank, it says "you're too small - I like to
take my sweet time schmoozing with very rich people".

hhp

I'm impressed by the number of logos I'm seeing in conservative old fashioned serif typefaces. The image they project is "nothing dicey here". Just what you want for somebody handling your money. Adobe Caslon was one.

You need to pick something that’s already used by their established, credible, trustworthy competitors.

LTR Federal?

Theoretically, the most credible and trustworthy font would have no asterisk glyph and have some kind of script that prevents it from being set at less than 7 pts.

Also, I was going to suggest Franklin Gothic--which for whatever reason had always seemed trustworthy to me. Then I remembered Bank of America.

Enron Beelzebub