T&Cs are vital. Under the Consumer Protection (Distance Selling) Regulations 2000, the buyer does not even need to return the goods when he exercises his right to cancel and becomes entitled to his money back (I know your case was an agreed exchange but this fall back risk remains) unless the T&Cs state that he must do so.
He has a statutory duty to take care of the product so returning without the box risks liability for damage.
"The website right now is for retail customers, and trade customers use it just for reference. "
Mixed visitors can be a problem. If trade customers are clever they can increase their statutory rights by claiming to be retail customers, although they might lose the VAT invoice dependent on how your trolley operates. To reverse this effect, good navigation/content can reduce your cancellation risk from consumers by encouraging them to claim to be business users (eg by discounted pricing). This policy exploits the fact that the statutory definition of a 'consumer sale' is subjective -ie what was that particular buyer's purpose in buying the item. So if he says it was 'business' its going to be hard for him to subsequently deny that in order to exercise consumer rights. Many products have joint use eg did the dentist buy the digital camera to occasionally photograph his patients' teeth or as the family camera?
It does seem that a number of people are doing business T&C-less so look out for an offer from me on UKBF that you are welcome to take me up on
