What makes an ad agency reliable to you?
One in which all of the employees are encased in carbonite, and whose computers and records have all been nuked from orbit.
Anything less and you have to assume they're still unreliable.
And what solutions do you recommend for individual blog authors to implement "host your own ads"?
Not Our Fucking Problem.
Sorry, but I will continue assuming all ads are crap I don't wish to see, served by companies who don't give a crap about my privacy or security and whom I therefore do not trust.
The revenue of web sites interests me not even a little.
Go to a subscription model and see if you can stay in business. Or accept that some fraction of users do not wish to see your advertising, and don't trust the companies serving them.