It is certainly touching to see such lengths being explored, even to the extent of possible DNA testing, before choosing a suitable tartan to wear. No doubt this is either out of a desire to explore one's roots or from a respect for Scottish customs and traditions. As to actual clan membership, however, unless one is a clan chief or a close relation of one with a proven genealogical record I doubt that there is any real way of proving descent from amember of a particular clan. A surname helps to point you in the right direction and no-one is going to dispute your right to wear the particular tartan that your name relates to. That alone, however, is no proof of clan membership as people often moved about the country for various reasons such as persecution, work etc. and, as nobody actually 'joined' a clan or was entered in a 'membership list' like joining a golf club there is little more than a possible association with a name and locality to rely upon as the best you can do to decide.