Some of the disadvantages can be that once you have bought the data or spent time searching for it, it may not be exactly what you need, it may not cover what you need it to. You will not know if the data was bias or not as you may not know where it came from. The research of secondary data can give good guide lines as to how you may want or need to carry out your own primary research. It can give you ideas on what types of questions should be asked, but more importantly it can help you decide what type of research to carry out, should it be quantitative or qualitative and also how to define and measure and quantify the answer into meaningful results.