Don't just use one database when performing searches. If there is another site that indexes the same data, their index might allow for different searches or might have included transcriptions done differently. You might not have to subscribe to one of the pay sites "forever," but make a list of things you can't find on the free sites and consider subscribing to a pay-site for maybe a month and doing your searches and then let it expire.
But never rely solely on one site for all your indexes.