Is this a good idea? Especially if the agency has never posted before, just opened up a Proz account, and has no Blue Board or references?
For the rest, the employer looks like a genuine, with company letterhead, good contact information etc etc.
Is this something you can do as a transaltor in the translations field and not be frowned upon, or worst of all, declined for the project?
The idea behind is that you don't leave empty-handed in the case of a scammer.
Any input welcomed.
I would put it this way... If you don't know the agency, they have no proven track record, nothing except good letterhead and paperwork (which even Nigerian scammers are pros at), then you are safe to ask for a deposit, and it may not be actually so small at that.
Once they have paid you well and in time, have established a good track-record, you can place them on the BB and testify to their genuine nature - sure, we all will happily take whatever jobs they have to offer without any deposits.
But at this point - not just yet.