Depends. ideally it is a sector you are very familiar with and in such a situation, you should be more familiar than so called experts in the market. In these cases, you will still use third parties if the CDD is very laborious such as huge geographical coverage of multi cities, mystery shopper, undercover investigative work etc.
If you are a financial investor and not an expert in that industry, I would usually first rely on public research to get a first cut before deciding how to approach CDD and how to budget the right costs.
