Sounds like you know this already, but it may take some time (or not depending on the quality of your offerings) for your clips to move up into the first search results. Each sites engine is homemade, so they work differently but, they are triggered by a few events with determine relevancy. The first one mostly likely being - have you sold clips on the site before. The search is probably weighted in a combination favoring proven sellers both as a clip and as a seller. The second being the ratio of views to sales, which is the same thing, but in reverse - many hits and no sales decrease your relevancy. It's hard to peer into the search engines, as they are not giving up their secrets. A combination of strong key-wording, sellable footage should tell you something over time.