Watertight proof of infringement of 500 ft rule is not easy to come by. Prosecution is rare and successful prosecution rarer(Have there been any?). With normal instruments even the pilot cannot be sure of his exact height, let alone those on the ground. Fly sensibly (it sounds like you do) and dont worry about it. The path of least resistance is to accept the clearance and nail it at 500ft.
edit:
Even if you are at 300 ft AGL the complainer has to prove your track was within 400ft of his property, and what your height was, to get anywhere near a rule 5 infringement. (remember 3,4,5 triangles!)
Last edited by Gaseous; 15th Sep 2007 at 16:34.