Is there no circumstance in which you could recommend an agency?
The unspoken assumption underlying assignments is that if it were ever to come to the crunch, quality control is the client's responsibility, not the agency's.
Agencies are particularly useful for multilingual projects where the translation of a document or set of documents into a dozen languages is primarily an administrative requirement, i.e. where the quality control aspect is conveniently swamped in administrative complexity.
Agencies maintain registers and databases that allow them to offer ‘medical translation' between a wide variety of language pairs. The unspoken assumption underlying such assignments is that if it were ever to come to the crunch, quality control is the client's responsibility, not the agency's.
Common sense indicates that an agency cannot in good faith claim quality control over such material except in terms of general presentation.