Replying to [Panny]: Yes. That's should be a norm for exhibitions' response. Because hundreds of booths a visitor visited during a trade show, he might need to filter the collected information and response to only limited few that he really interested. Secondly, some potentials not really genuine as he showed during the Show. Third, the follow-up emails that you sent might not impressed him.
Normally, if you can get 10% response out of the total leads, it should be quite good already. From the 10%, if 5% can translate to become your customers, it should be considered a good result. If one out of the 5% is a big client, it's a celebration!
Sometimes, the leads will come back after a long time. Too aggressive and keep on sending emails in a short period might create irritation to potential buyers, unless you can make sure your everytime your email will bring joy to him.