I do not see the problem, With the advice given to me by the person who did my EPC, i have a good guide to where D band would be. Clarity and Honesty has won me more work than it has cost me. Basically i will look at it and explain the situation to the client, giving them the info i know, and if they agree in principle to place the work with me i will have the survey done. It will be mine untill the works are done. If the property fails to reach band D without vast expenidture to the client and they choose not to go ahead, thats my loss, but i really feel that if you explain to the client what its about, there will be few issues.
I will not charge the client up front for it, but it will be built into the cost of the job if it goes ahead.