How to manage price when not enough details are provided by the client

[#1]

A lot of clients propose jobs with very little or no information about it, so that it is very hard to decide what a fair price would be for the job (I work in consulting and software development).
Usually more details are provided after a proposal is submitted, and for that I usually propose a dummy price to be fixed later, however in theory the client could hire me for that price right away and then I would be boud to do the job for that price. What would be a good way to approach this issue?

Thanks!

[#2 · Accepted solution]

The client can't just hire you at your placeholder price without you accepting the offer. When I hit this issue, which is often, I state clearly in the proposal that the price is a placeholder and I need to review the material or need additional details before I can give them an accurate quote. I've never had someone just send an offer at the placeholder price after that, but if they did, I'd ask for whatever I needed to know and then if the price has to change, reject the offer and ask them to resend it with the correct price.