For an E4 the only requirement is that there is a paper trail to the end user, i.e a delivery address and name.
For a 320x240 pixel 60fps camera, a seller has to complete some paperwork, submit it to the appropriate authority (BIS in USA?). A licence is then issued for export out of the USA to the licenced recipient. Export without the licence is a federal offence which is why you will see US sellers only shipping to US Citizens in the USA. They don't want to risk any problems with their government. Others are unaware of the regulations and innocently ship equipment. On an individual sale, action is unlikely. If you were to sell a thousand without a licence the situation would likely be very different.
I know of no prosecutions for selling thermal camera technology without a licence. I am aware of a case in the UK where a chap was dealing in high technology weapons grade batteries and wishing to ship to an inappropriate customer without the required licences. He was extradited to the USA and I believe he is serving 3 years in prison as a result of his actions
http://en.wikipedia.org/wiki/Christopher_TappinFLIR do all the licence applications etc. as part of a purchase. The licence requirement is often lost/ignored on the used market. Other companies charge quite large sums of money to do the licence application etc. I have seen $300 charged.
Selling into Europe is straight forward especially if its is a single item. Selling into areas of international tension could be a little more challenging as the recipient of the technology needs to have a traceable security footprint.