Related question: what are your policies on keeping a tentative booking open for someone?

A few weeks ago someone asked me if I could play a St. Pat's gig on March 11 or 18 - she wasn't sure yet which date they would have the party. I said that I was available either day, and she said she would let me know, which she hasn't yet despite a couple of reminder calls. Now someone else has asked me if I'm free the 11th.

I realize now that I should have made it clear with the first place how long I would keep those dates open for her, especially so close to St. Pat's.

So I'm looking for advice on two things: what to do in this situation, given the mistake I've made; and what the best approach is for the future. Refuse to commit to anything until they've committed to me? Make a policy that I'll hold a tentative booking for a certain amount of time (how long?) after the initial discussion, or before the date in question?

Thanks, Marion