1. Beware of language schools-cum-translation agencies.
The best you will generally get from them is "native speakers".
2. Beware of agencies that translate birth and marriage certificates, school transcripts, etc.
If they were competent to do high-level work, they would not be working at the bottom of the profession
3. Beware of non-translators acting as translation brokers.
I have known of a radio announcer, a carpet layer, a piano teacher, and a make-up artist, among others, who have opened "translation agencies". They usually stay in business long enough to do a lot of damage to unwary clients. The usual procedure for these ventures is to run a "translators wanted" ad in the paper to acquire a list of freelancers. Then they put some money into advertising and wait for the clients to be lured into the trap.
This is a typical yellow pages advertisement for an all-too-common type of agency:
"Legal / Medical / Technical, etc. / Simultaneous and Consecutive Interpretations/ School Transcripts / Diplomas. See Ad at Language Schools."
Why don't we show equipment prices on our website? Our prices are so low that the manufacturers don't allow us to advertise them.