I think in helping them visualize a design with some sketches would be considered 'marketing' and an investment you would make upfront. Should those drawings be turned into a detailed plan that someone paid for it would become the property of the purchaser based upon T&Cs.

I see plans on the net from reputable framers allowing the purchase for a 1 time construction etc. This is different than paying for a custom design and all associated time for the custom design. In the latter case I would expect the design to become property of the purchaser.

I always appreciate your posts Clark but honestly I think it may be best to let this go as a lesson learned. When providing a preliminary drawing dont provide any dimensions or timber sizing etc. If the customer needs that level in a printout or file there is no reason a deposit could not be provided for the design effort to date.

Dont want to sound harsh here in tough economic times...but you provide PREMIUM service and hopefully they will come back and recognize the value in working with a top notch company smile

Did they do an unethical thing? Hard to say based on what is going on in their mind. Some people live by the letter of the law, others based upon sound moral principles.