We all had a situation when the client sends a paper with questions where you have to spend a couple of hours replying. Then he replies back with more question, and again you spend a couple of hours replying. Even after that you have to spend some hours investigating technology he mentioned in order to give him a better proposal.
Now, where is the limit here? So far, I was unable to find a good way to tell him that I cannot do so much work during estimation for free. In such situations, I told my clients that such details will be discussed when he has awarded me the contract, and 98% of then never contacted me again. Maybe they were not serious, maybe they wanted free info from me, maybe...
The other cases finished in a way that a client stopped replying to my emails.
Either way, I feel abused without being able to find a way to deal with such clients.
What do you do here? How to satisfy the demanding client and get the job, and at the same time have all extraordinary work hours covered?
PS. I tried to find a question on this topic here, but I saw only similar ones. All similar discussed situations when you're already hired. None mentioned negotiation (estimation) phase.