The whatisyourrate question is a noob trap, for the only meaningful answer is “I’ll know it when I see it.” However, with proper jiu-jitsu the come-on can be given useful meaning and turned to your advantage.
The true answer for a countable word processor file assumes I can do X words per day with a probability P of mine being the best bid. If X is over 3000 words and P exceeds 0.5 (even money), the job is worth bidding on even if a middleman is involved. To know these things I have to see the material, but trappers who want translators at a disadvantage seek to exploit an information asymmetry.
First we have the “standard of value” approach, which takes “what is my rate” and adds “compared to what I normally do.” I normally do oil and mining contracts and bidding documents and agribusiness reports. So if a middleman wants an unseen something that’s different I can answer “twenty percent over the standard market rate for an oil RFP.” THEY have to either know that the market rate is–that’s the middleman’s job–or produce the document. Either way they’re not wasting my time. No middleman can hire you for stuff you’re not good at and then sell it at a profit. This goes back to the probability of a sale. If that is a bad bet, then why bother bidding?
The “just sign here and we’ll get started” approach is also easy to dribble. People send me all kinds of unenforceable, unsigned drivel. The unsigned stuff goes in the trash. Until a document gets two signatures on it it is worthless. Getting only you to sign something makes it not binding on them. But they can sign at a later date to make it binding on you if convenient. Much of what I see looks illegal under antitrust laws. Criticising is a waste of time, so I send them my signed NDA which they can return with their signature (which makes two), along with the document needing a bid.
As a construction contractor I developed bidding spreadsheets. Anonymous contractors kept calling for guesstimates and never hired me. It dawned on me that I was doing their work for free, so I started asking for the job address. Those WIYR calls ceased immediately, freeing my time to deal with real clients. The lesson applies to translation. Fully half the calls from “Fred” or “Ana” are calls from wannabee translators pretending to be agencies so they can learn what the market will bear.