What sort of questions can I reasonably ask before agreeing to meet a potential client?

[Legacy]

I often meet potential clients through industry events & conferences etc. There's the usual swapping of cards etc and vague promises to meet.

Someone I met through a conference in June has just e-mailed me saying he's in London and would like to meet 'to discuss a project'. The thing is, I don't really know much about his company (website not working) and I don't want to trail into London to find that he's just trying to extract knowledge from me with no real potential work at the end of it.

I was thinking of e-mailing him some 'advance' questions to see if I can assess whether he's 'genuine' or not - would this be rude do you think?

Or do you think I should be trying to 'semi-interview' him first by phone?

I would call or email in advance, and say things along the lines of "yes I'd love to meet - can you tell me more about the project you have in mind?". Probably easier to extract info on the phone, and then you can always cancel the meeting later citing too much work etc.