I've created a single state workflow with one saved search to automatically email customers. I put a checkbox on the transaction record Email Sent if unchecked the workflow will trigger and send the email and then check that flag "Email Sent". Apparently it's now sending twice to the same customer when it should have been checked once. Is thier a reason why I'm sending the same individual 2 emails.

Whats the context and Event

It's a scheduled workflow and it runs every 30 minutes.

hmm. I have a similar workflow, but I am using a mass update to trigger it by checking the box