I feel your pain. I did have that happen once and it was horrible. I felt so bad for this lady who thought she'd ordered a cake, but there was nothing I could do. She called me from the venue wondering where I was. When I looked back at the emails - she'd never even given me a date and time.
So now I have a paragraph of general ordering info that I send to anyone who sounds like they may order. I highlight it in pink, but still not everyone reads it. To solve the problem of it not being read, whenever someone replies with an answer like, "that's all sounds great", I'll send it again saying, "below is general ordering info so you'll have it when you're ready to order".
I've been looking for an app that will literally jump out of their computers, grab them by the collar, make eye contact and yell it at them, but have so far come up empty handed.